Unless you're headed for an iron man in the next year or two, I'd really recommend a well fitted road bike with removable aero bars. A tri bike is very limiting, you can't do other races with it, and most group rides prohibit (or discourage) using tri bikes, and you can't use it for touring.

There are some really neat tri bikes out there, but unless you're sure you don't want to do anything else, a road bike is the way to go.