I think a lot depends on the bandwidth and hardware requirements of the games you're running, and the datacenter where the server is located.
I've used GameServers for quite some time, but lately the service in the Dallas datacenter has been horrible. Chicago is *slightly* better, but even as I type this my Chicago based UT server is down due to unknown issues. If I didn't have my high bandwidth servers there at $.049 / $0.75 per slot, I'd move them elsewhere.
For my less played servers, I just host it on my two 50/10 business lines. Not the greatest pings, but I've had over 100 players connected at a time without any real issues.