I own at least a half-dozen suits... unless you need more than 2, don't bother going to the mall. Jos A. Bank is "ok" if you need multiples and want to do their "buy 1, get 3 free" deal....but otherwise, there is no reason to go to any mall-attached department store. You're just overpaying.
If you only need 1 suit (black, I'd presume) and won't be wearing it all too often and it doesn't need to last until it goes out of style, just go to K&G and find one off the rack, have them tailor it (should be included in the price) and save your money. You should be in and out for under $200 at K&G, no problem.
To asmo's point, if you don't know what you're doing, you could always go somewhere, ask some questions, try on a few suits and then go to K&G... but if the service is great, you may want to pay for it, too....