my 07 kx450 had a 250 like pwerband, just a bit more and it hooked up better. the 09 450 is way smooth almost to the point of feeling a bit short on power, not so, it pulls from nothing to forever.
I've also got a 06 250 2t, I don't like it, for a trail bike I like the 250f, I've had 5 250f's and loved them all, I don't currently have one but as soon as I get rid of something I'm going to get another just a fun bike, and they have good power, not hillclimbers but they'll pull you around up some pretty steep stuff.
bottom line, personal preference, you won't go wrong with either.