Why is that? UM seems to be the cream of the crop. Very aggressive though.
It all depends what you're looking for. If you want to just flash it and forget it, there are a lot of good options, but none of them will really optimize the tune to your exact vehicle and your personal preferences.
With ED and Cobb being so versatile, customizable, and priced so close to the one-size-fits-all offerings from many other tuners i just don't see much reason to buy a generic tune. They're as mild or wild as you want.
ED has end user tuning/flashing, e-tuner options, and the ability to modify all of the important parameters. Support for MPI if you ever go big turbo, DSG tuning, etc. All the critical stuff is there and it's all customizable, and offers infinite headroom with little to no additional cost.
Cobb has a simple and convenient handheld which flashes in about 2 minutes, good logging capabilities, OTS tunes to mess with, a variety of e-tune/protuner options, awesome ignition based traction control (for us FWD guys), excellent resale value, etc.
Both of those options require more involvement to really be worthwhile. They can be set it and forget it, but the real benefit comes from the additional capabilities they offer.