I have a KLR250 (predecessor to the KLX250S, in a way) and now also a KLR650; obtained in that order.
An undeniable fact; a 250 is EASIER to pick up than a 650! (Even backing up to it and doing the "dead lift" routine, the "baby steps," and so on.)
While the 650's the choice, when tooling down the pavement, I'd have to say the 250's the more versatile.
Yet, you can't go WRONG with either.
Then again, if I were shopping for a 250, I'd have to take a look at the Yamaha WR250R, today; fuel injection, advanced suspension over the KL's . . . YMMV!