I enjoy using XFire. To me it is in every way better than Steam's community chat. Its overlay is snazzy, it comes with little tackable overlay sections, like FPS, a Clock, hell, you can even pin the chat up if you want. You can also use it to record videos, broadcast live, take and upload screenshots, and it has a built in music player. The video codec used to record video compresses extremely well with very little loss. A five minute 1280x1024 video runs about 30-50 megs on-disk.
Like Steam, it also does chat, keeps track of game time, has a web browser in the overlay, and does VOIP. But what Steam doesn't have that almost all other chat apps do, is P2P file transfers. As long as you're not an idiot, you wont be accepting every single file transfer that comes in and get yourself a virus, so people who say that's a security hole are a tad off.
However, out of all that, the best thing I like about XFire over Steam: I can actually HEAR the in-game chat alert. The recent Steam updates replaced their once-audible "DEHDOO" with a tiny, almost polite little "bloop" that you CANNOT hear unless you're either wearing headphones or are not in the heat of battle at the time.