I went with the Magnaflow kit. Has a very nice sound to it at startup (enough to let you know it isn't stock - sounds like a truck should)...when you get on the skinny pedal, it sounds real nice...not a raspy, raucous sound, just a nice muscular V8 sound. But the best part is when you are cruising, it is not much louder than stock - no drone! Believe me, in my Camaros and GTOs, I loved the Flowmaster noise all the time, but for the Tahoe I wanted something mellow with a little more noise on the outside, and not much on the inside - the Magnaflow is exactly that.
Also, fit and quality of parts supplied was excellent, everything went together just fine - took me just over an hour to cut the stock exhaust out and install the Magnaflow...looks awesome in its stainless steel (muffler is actually POLISHED stainless!) - too bad it is hidden from view. Real nice tip also.
I'm very happy with mine, I'd recommend it. I've only noticed a slight increase in MPG, but that is probably because I have been driving it just a tad more enthusiastically to enjoy the rumble!