I agree with everyone saying that one of my biggest drugstore fndtn gripes is the limited color selection. Though I've found numerous foundations that were good, IMHO they don't really compare to dept. store/expensive foundations. Granted, there are a few diamonds in the rough at the drugstore though LOL!
It also matters if you find the best formulation for your skin. Drugstore or not, if the formula sucks for your skin, you'll hate it. I would say thats the first step, determining what you're skin needs/wants. Then, try and find your shade in the d/s, etc.
I for one love buying higher end foundations because it's easier. You can talk to someone who understands your needs, and get a great match (usually). Going to a d/s and finding one takes more time IMHO.
Also depends on how much you'd like to spend. 30 dollars is my limit for ANY foundation, cuz if I spent anymore I'd be broke! There are some good ones between 18-30 dollars. I hope this helped a little bit!