We moved back to the St. Louis area from Texas, where they didn't have Aldi's in late 2006 and it my favorite grocery for staples, especially! I am not very brand specific, so I have never really noticed a difference in that aspect. You can't beat their prices on milk, eggs and such and I love the Fit & Active line. I always stock up on my frozen fish fillets, chicken tenders etc. and love their "seasonal" offerings. You never know what bargain you might find!
The only downside is the selection....if you want pasta, you get 3 or 4 choices etc. so I do a Shop & Save run every couple of weeks to get what I can't find at Aldi's and the few name brand products I like. As for WM, I find that their groceries are not competitively priced at all any more. S & S and Aldi's are MUCH cheaper.