I don't do tons of discount store shopping, but here are my takes:
Kohl's: I don't buy clothes there all that often, but when I *do* find something, it's usually a great deal. Plus they have some cute jewelry sometimes.
Ross: Hate it. The ones near me are always so messy and disorganized that I usually give up in about 10 minutes and head to the mall. Plus, it seems like they just don't carry clothes in my size (0P or 00P).
Marshall's: I have the same feelings about this one that I do Ross. The stores I've visited are a little more organized though.
JC Penney: I don't really shop there for clothes.
Old Navy: Hate it. The quality is almost universally awful and their sizes run super big on me. I DO have one pair of jeans from there; they were too long when I got them, and now, after repeated washings, they are pretty short. bad quality.
Target: Personally, I love their juniors Mossimo jeans. They fit me great for some reason. I also like them for things like basic tanks. Their juniors department also sells some very cute tops. Occasionally they have decent sweaters, too.
DSW: I LOVE DSW. The ones near me are large, organized, and have GREAT prices on name brand shoes. I also like Off Broadway shoes.
Payless: I hate this store. Their shoes all run super wide for me (although they might be okay if you have wide feet). I find their quality lacking as well.
I also like to shop at Goodwill. Not that I find much, but when I do find things, they're super cheap! And if you find a quality item that doesn't fit the way you like, you'll have money left over to take it to the tailor.