XLink Messenger is the new Xbox Tunnel program out on the streets. Not only does it sport a sleek look ( http://members.cox.net/gamma/xlink.jpg ) it also plays games great, and in my opinion better than XBC. No start up lag in Halo anymore . Also they've included a few of their own features in the software that no other program has. They've got this mode called "WGN", where users can switch to this host a game, any anyone else in WGN mode can see this game. This eliminates the need for rooms and the annoying searching for a good game... no running from your PC to your Xbox. It also has rooms mode for those who like that though :P. Messenger mode allows you to chat with your buddies and play with anyone on your buddy list...
Brute Force supports 4 players via system link, where XBConnect only supports (and will only support 2), and the same goes with GameSpy tunnel. Only downside to this program right now is lack of users. There's only 50 or so users on minimum, where other clients have 200 minimum. This can change if people try the client out and stay with it. Oh yea, uses less bandwidth and has packet caching. WET11 support too, take that XBC!
BTW I'm trying to get a Halo fest organized tonight at 10:30 EST, add GaMMa to your buddy list on the program and I'll be on then to get a bunch of games organized.