Flour preferences

I find both of these flours pretty comparable, however the protein (and gluten) content of the King Arthur flour is going to be a bit higher than the comparable Gold Medal flour.

I haven't had much success with Gold Medel's AP flour, but the "better for bread" flour is quite acceptable.  Of the two AP flours though, I like the King Arthur a bit more.

Personally I use Central Milling's "Type 70" high extraction flour for pretty much all my bread baking.

but I think that should you start buying full on bottom shelf supermarket brand flour you might notice a difference in quality and almost certainly in consistency... my personal philosophy towards picking flour has been if I am spending two days on a loaf or two of bread I totally will spend the extra thirty of so cents to hopefully ensure that it acts the same as it did last time.

 For what its worth, I almost always use king arthur for my AP and Bread flour and I use bob's red mill for the other more specialty stuff, and if possible I get stuff from smaller local mills as well.

Of U.S. supermarket wheat flour by protein/gluten content:

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U.S. WHEAT FLOUR TYPES AND BEST USES:
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Wheat Flour Protein:
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-Protein levels range from about 7% in pastry and cake flours to as high as about 15% in high-gluten bread flour. 
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-Protein percentage indicates the amount of gluten available in the a given flour. Gluten is the substance which develops when the flour protein, which occurs naturally in wheat flour, is combined with liquid and kneaded. 
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-Because gluten is able to stretch elastically, it is desirable to have a higher gluten flour for yeast-raised products, which have doughs that are stretched extensively; like pizza, most yeast breads, and bagels. 
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-For cakes, pie crusts, cookies, biscuits, pancakes, waffles and pastry to be short and crumbly or tender, a lower protein flour is better. Also, in higher gluten flours, the gluten can overpower the chemical leaveners like baking powder or baking soda, causing the final baked goods to not rise as high.
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-Hard winter wheat, mainly grown in the north, has a higher protein and more gluten, 10% to 13%. 
Most northern and national brand all-purpose flours, bread flour and high-gluten flour is made from hard winter wheat.
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-Soft summer wheat, mainly grown in the south, has a lower protein and lower gluten, 8% to 10% 
Most cake, pastry and southern all-purpose flour is made from soft summer wheat.
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Bleaching flour does a couple of things, it whitens the flour and it also alters the flour protein causing it to form weaker gluten. Most cake flours are bleached.
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FLOUR PROTEIN BY TYPES AND BRANDS (retail flour):
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CAKE FLOUR - 7% to 9.4% protein
Best Use: cakes, blending with national brands all-purpose flour to make pastry flour or Southern flour substitute.
-King Arthur Queen Guinevere Cake Flour, 7.0%
-King Arthur Unbleached Cake Flour Blend, 9.4% 
-Pillsbury Softasilk Bleached Cake Flour, 6.9%
-Presto Self Rising Cake Flour, 7.4%
-Swans Down Bleached Cake Flour, 7.1%
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PASTRY FLOUR - 8 to 9% protein
Best Use: biscuits, cookies, pastries, pancakes, pie crusts, waffles.
-King Arthur Unbleached Pastry Flour, 8%
-King Arthur Whole Wheat Pastry Flour, 9%
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ALL-PURPOSE FLOUR, SOUTHERN - 8 to 9% protein
Best Use: biscuits, cookies, muffins, pancakes, pie crusts, quick breads, waffles.
-Martha White Bleached All-Purpose Flour, 9%
-White Lily Bleached All-Purpose Flour, 8 to 9%
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SELF-RISING FLOUR (flour, baking powder, salt) - 8 to 10.5% protein
Best Use: biscuits, cookies, pancakes, muffins, quick breads, waffles. 
-Gold Medal Bleached Self-Rising Flour, 10.5%
-King Arthur Unbleached Self-Rising Flour, 8.5%
-Martha White Bleached Self-Rising Flour, 9.4%
-Pillsbury Best Bleached Self-Rising Flour, 9.7%
-Presto Self Rising Cake Flour, 7.4%
-White Lily Bleached Self-Rising Flour, 8 to 9% 
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ALL PURPOSE BAKING MIXES (flour, shortening, baking powder, sugar, salt) - 6.25 to 12.5% protein
Best Use: biscuits, cookies, coffee cakes, pancakes, quick breads, pastry, waffles
-Arrowhead Mills All Purpose Baking Mix, 12.5%
-Bisquick Original Baking Mix, 7.5%
-Jiffy All Purpose Baking Mix, 6.25%
-King Arthur Flour All Purpose Baking Mix, 10%
-Pioneer Original Baking Mix, 7.5%
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INSTANT FLOUR 10.5 to 12.6% protein
Best Use: thicken gravies, sauces, and soups without lumps.
-Gold Medal Wondra Quick Mixing Flour, 10.5%
-Pillsbury Best Shake & Blend Flour, 12.6%
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ALL-PURPOSE FLOUR, BLEACHED & UNBLEACHED, NATIONAL BRANDS - 10 to 11.5% protein
Best Use: makes average biscuits, cookies, muffins, pancakes, pie crusts, pizza crusts, quick breads, waffles, yeast breads.
-Gold Medal All-Purpose Flour, 10.5%
-Pillsbury Best All-Purpose Flour, 10 to 11.5%
-Pioneer All-Purpose Flour, 10%
-White Wings All-Purpose Flour, 10%
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ALL-PURPOSE FLOUR, NORTHERN, BLEACHED & UNBLEACHED - 11.5 to 12% protein
Best Use: cream puffs, puff pastry, yeast breads, pizza crusts.
-Heckers and Ceresota All-Purpose Flour, 11.5 to 11.9 %
-King Arthur All-Purpose Flour, 11.7%
-Robin Hood All-Purpose Flour, 12.0%
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BREAD FLOUR - 12 to 13.3% protein
Best Use: traditional yeast breads, bread machine, pizza crusts, pasta.
-Gold Medal Better For Bread, 12% 
-King Arthur Unbleached Bread Flour, 12.7%
-Pillsbury Best Bread Flour, 12.9%
-White Lily Unbleached Bread Flour, 11.7%
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DURUM WHEAT (Semolina) 13 to 13.5% protein
Best Use: Pasta.
-Hodgson Mill Golden Semolina & Extra Fancy Durum Pasta Flour, 13.3% 
-King Arthur Extra Fancy Durum Flour, 13.3%
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WHOLE WHEAT FLOUR - 12.9 to 14% protein
Best Use: hearth breads, blending with other flours.
-Gold Medal Whole Wheat Flour, 13.3%
-King Arthur 100% Whole Wheat Flour, 14%
-King Arthur 100% White Whole Wheat Flour, 14%
-Pillsbury Best Whole Wheat Flour, 12.9%
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HIGH-GLUTEN FLOUR 14 to 15% protein
Best Use: bagels, pizza crusts, blending with other flours.
-King Arthur Organic Hi-Gluten Flour, 14% 
-King Arthur Sir Lancelot Unbleached Hi-Gluten Flour, 14.2%
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VITAL WHEAT GLUTEN FLOUR, Breadmaking Supplement - 65 to 77% protein
Best Use: Added to raise gluten. Adds extra gluten to low-gluten whole grain flours, such as rye, oat, teff, spelt, or buckwheat.
-Arrowhead Mills Vital Wheat Gluten Flour, 65.0% 
-Bob's Red Mill Vital Wheat Gluten Flour, 75.0%
-Gillco Vital Wheat Gluten Flour, 75.0%
-Hodgson Mill Vital Wheat Gluten Flour, 66.6%
-King Arthur Vital Wheat Gluten Flour, 77.8%
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Retail Flour Companies - Brands:
-Bob’s Red Mill Natural Foods, Milwaukie, Oregon -Bob's Red Mill 
-C.H. Guenther & Son Inc, San Antonio, Texas - Pioneer Flour, Pioneer Baking Mix, White Wings Flour
-General Mills Company, Minneapolis, Minnesota - Bisquick, Gold Medal Flour, (sold US Pillsbury Flour , retains Pillsbury frozen goods)
-Hain Celestial Group Inc, Boulder, Colorado - Arrowhead Mills
-J.M. Smucker Company, Orrville, Ohio - Martha White Flour, Pillsbury Flour, Robin Hood Flour, White Lily Flour
-King Arthur Flour Company, Norwich, Vermont - King Arthur Flour
-Reily Foods Company, New Orleans, Louisiana - Swan's Down Cake Flour, Presto Self Rising Cake Flour
-Uhlmann Company, Kansas City, Missouri - Heckers Flour, Ceresota Flour
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  I have great success using any brand name AP flour - Gold Medal unbleached, Pillsbury unbleached, King Arthur, Ceresota, Dakota Mai. They are all available around here in the heart of the Midwest- southern Wisconsin.

 I have discovered only 2 flour products I will NOT use for bread:

   1. any bleached flour and

   2. Roundy's brand (bottom shelf store brand) unbleached AP flour.

The key to using an AP flour when making bread is to make sure you have a little higher hydration and to make sure you develop the starch and the gluten in the mixing/kneading process. Go for a good windowpane.

I use KA AP & Bread flour (unbleached). I also use Wheat Montana's Prairie Gold white whole wheat and Bob's Red Mill Dark Rye. I real like the flavor profile I get using these flours.

I've tried bread made with Gold Medal but didn't care for the flavor.

A close second to KA flour was Pendleton Flour Mill's Morbread AP and Power Flour high gluten flour. I just didn't like the flavor profile as much.