Our 32 slot TF2 server is through
www.FragFestServers.com. The people there are absolutely incredible, namely Broseph. There's no way I could say enough good things about these guys from the price to the quality.
I've had servers at:
www.GameServers.com - Decent basic servers. Moved away because they only offered 24 slots and I prefer TCAdmin.
www.Branzone.com - Our first 32 slot TF2 server host. Great people, but we needed to shave a few bucks off our monthly bills so I took a leap of faith and moved to
www.fragfestservers.com .
www.XFactorServers.com - Our L4D2 server host. The issue with these guys for us is that our servers have twice been shut down shortly after I get an e-mail stating I'd made an unallowed change to the server's configuration by increasing the slots from 8 to 16 which is ridiculous when we don't even have that kind of command line access. We'll be moving L4D2 servers to FragFest soon.