I was a mixed bag on TBs for a while, but that's because I've ridden all types. It's like any breed of horse really--you have your hot ones and your been there done that type that's pretty cool and quiet.
I plan on rescuing an OTTB when I have sufficient funds, they are gorgeous horses and make great english sport horses--I want to do eventing with a heavy focus on dressage, and most of the QH's around here just don't cut it (although I've seen the rare jumper QH, most of em around here are born and bred trail horses), and where else can you get an amazingly gorgeous talented horse with a great pedigree at a rescue?
Make sure you know whether you want a mare or gelding ahead of time, try to ride a few different ones so you can find which you click with. My first horse was a mare and that taught me that I don't get along with mares particurally well, so I'm going for a gelding next time around.
Other than that follow everyone else's advice, get something you think might be a little calmer than you need, because a common first buying mistake is to buy something too green and only realize it when you get home. Don't get over ambitious, and take the advice of your trainer. Good luck! ;)
It's a dangerous business, Frodo, going out of your door," he used to say. "You step into the Road, and if you don't keep your feet, there is no telling where you might be swept off to."