sourdough V yeast ?

I'm not an expert in any way, but here is a quick answer to start you off. Sourdough gives a lot more flavor and better nutritional quality to the bread because of long fermentation. You could do the same with yeast, but it would actually be more challenging than just using sourdough. Yeast is better if you need to make your bread a lot more quickly. It is also fine for breads where the flavor is meant to come from added ingredients such as sweet breads (sugar, fruit, honey).

Each produces breads with differing characteristics.  Even within the sourdough realm, flavors can range from sweet to intensely sour.

Here are some general observations.  Either can serve to leaven bread effectively but the sourdough will usually take longer to do so than will commercial yeast.  Sourdough, because of the lactobacilli in the culture, can produce flavors that aren't available in breads made with commercial yeast.  Wild yeasts in sourdough tend to slow down even more in cool temperatures than do their farmed cousins.

"Better" can only be assessed in the sense that you may be able to produce an outcome with commercial yeast (speed, for instance) that you can't with sourdough.  The reverse is also true, where the difference may be a desired flavor profile.

Paul

Both sourdough and yeast will act to leaven bread.

Sourdough produces acid and baker's yeast does not.  So, sourdough is good when you need acid, like for 100% Rye, or want the flavor the acidity produces, or other characteristics, like dough conditioning.

Baker's yeast is used when you want less acidity, it was historically referred to as "sweet" fermentation, it has a clean flavor profile which allows other flavors to be more noticeable or predominant.

or not you want a sweet or sour flavor profile in the finished product .  Lets face it most people don't like sour bread as much as they like non sour bread.  Neither is better than the other except that commercial yeast costs more money if you don't use it a poolish. 

For sweet breads like cinnamon rolls, i use yeast water which is a naturally cultivate yeast but has no sour component.like SD does.  In combination with SD YW also cancels out much of the sour bit you get the better keeping qualities and it still works for heavy rye breads to open the crumb and add the acid it needs.  YW also ferments at nearly same rate of SD so it isn't rushing ahead like commercial yeast will do to proof and ferment the dough too fast.

Happy baking

Commercial yeast, whether fresh, dried, or instant, is quite concentrated, so if you want your dough to rise quickly (or if it's loaded with add-ins) you can double or triple the quantity of yeast without changing the other ingredients very much. A yeast culture is developed in a nutrient broth, and then the yeast is separated from the liquid. Adding commercial yeast just adds the yeast without changing the hydration or any other part of the bread recipe. 

Sourdough starters, on the other hand, are cultured in a viscous mix of flour and water, and the yeast can't be isolated by centrifuging. Sourdough bakers are limited to developing the most robust population of yeast in their starter before adding it to the bread mix, but they are also adding both flour and water, which have to be compensated for in the recipe.

Most of us here don't have to bake on a production schedule, so we are more tolerant of the relative low activity of SD, and when we use yeast it's often in very small amounts mimicking the activity of SD. Of course, SD contains both yeast and bacteria, which many prefer for certain breads, and you will see complaints about some yeasted bread formulas that the resultant product is too 'yeasty'. 

In short, SD is a yeast-based leavening, with advantages and disadvantages. 'Yeast water' (YW) is another way to grow yeast, similar to commercial yeast but without the concentrating process. Even commercial yeast has differences in taste and behavior between the various forms. In the hands of a skilled baker any of the forms of yeast can yield excellent bread. Me, I'm still learning.