Road bike vs TT/Tri bike

A search on this topic will give you more than you ever wanted to know.

But I'll put a vote in for buying a tri bike. I ride my roadie to work and back and have to work to average 18mph. I ride my tri bike in the evening and I average 21mph with the same or less effort. Now of course there are always variables, but I for one find myself to be much faster on my tri bike.

If you:

ride with groups
have a lot of start and stop rides
ride a lot of real hills (>5-6%)
you might want to get a road bike

if you:

ride alone
go long periods of time without a stop sign, stop light or such
only plan on triathlons
You might want to get a tri bike.

The angle of the seat tube of a tri bike allows you to be lower in front and still have your hip angle more open. Read your gut isn't as compressed when aero.

A road bike with aero bars is probably more versatile but if you're only going to do tris and ride alone then that's why I have only tri bikes and just sold off a cyclocross bike I was using as my only road bike.