I've done a fair bit of research on this across many forums and best bang for your buck seems to be BDS and Fabtech with Pro Comp and Skyjacker coming in shortly after. Often, may of the complains I've read with any seem to be the shocks that came with the lift which was easily fixed with some better shocks (i.e.Bilstein 5100s or something else). I've not read a lot of negative about the rough country lifts, but I commonly hear if you're on a tighter budget, you can get theirs and be fine. Don't go for tough country.
Sadly, I don't have experience with them since I haven't lifted my truck yet, but like I said, I've been searching around a lot to make sure I get exactly what I'm looking for.
Another thing to keep in mind is what you'll be using it for. If it won't be offroad much, then any of the above should be just fine for you. If you're planning to be offroad, you might want to save up just a bit more and make sure you get the best one you can for your money.
Lastly, if you're sold on 6" (as I am) the above hopefully helps. If you're interesting in looking at 4" you can look at SST and Readylift as well. I've read decent things and you could save a bit of money. You should still be able to clear 34s with the 4" without a problem. At worst you might need some minor trimming. This would depend on your wheels, offset, etc..
Hope this helps.