I bought a T100 a little over a year ago and liked it so much I went out and bought a Tbird. The T100 was an absolute blast to ride and I wish I could have kept both. I decided that if I could only have one, it would be the Tbird. With the Tbird I can have fun going on short rides into the country but I am also comfortable riding 4-6 hours a day. I rode the T100 five hours a day on several occasions and did fine, but would rather spend that time something a little more comfortable. So a lot depends on the kind of riding you do. I love the Tbird but I sure do miss the T100. For pure fun, that was the best bike I ever owned. For all around, the Tbird fits the bill for me.
The only warning I can give you is beware, this may be one of those situations where whichever bike you own, you're going to wish you had the other.