I like little TBs, but there is definitely a trend for top riders on big young horses.
Really noticeable at Oasby - all the big names were out in force with their 5-6 year olds in the PN class. Collecting ring was full of big, floaty warmbloods.
I have a superb 15hh, and a 16.1, bith excel in different ways. The little one however is much braver than the big one, but then again i have had him longest so we trust eachother more!
I've got one 16.1 and one 17hh. The 16.1 is nippy and clever with his feet. And the big one gives you a huge sense of scope, as if you could jump a house, and covers the ground really well. But he doesn't (yet, only young) feel so clever with his feet than the ickler one.
The only thing I would say against the big one is that as he's so big striding, he can take strides out really easily, so in my very humble opinion, they are a bit harder work and you have to take the schooling very seriously!