It is debatable because most of these guys probably live in major populated cities where they are able to pick from almost any carrier and utilize the highest bandwidth possible on the phones.
I grew up on Sprint, but when I went to college, they had no service there, so we switched to VZW. Around my house, they are the best option, but I work in NoVA and go to Richmond a lot, so I could get another carrier since I am on WiFi at home anyways. I just haven't been that unhappy with them and my bill wouldn't be that much different to have me jump ship. I definitely will keep an eye out. I already if I leave, it will be for AT&T and nobody else though.
But yea Advanced Task Killer started off with a ton of hype, but then around 2.0/3.0, reports started coming out that it actually was worse for your phone. If I remember right it is due to the program just killing the apps/widgets/etc in whatever state they were in. Since it didn't gracefully close out the processes/programs, it caused your phone to work harder to essentially "put the pieces back together" (close threads, processes, & system files that were just left open even though they weren't in use)...I think