[prodigit]

For me personally, there's nothing like a small 150.
I'm happy with my evo150, probably would have been happier with a powermax 150.
200+cc's are a pain to work on. Especially when they have fuel injection.
They're complex, they weigh a lot, is almost impossible to get out of a crate alone or mount a front wheel.
Really, a 150 is the max I'm willing to buy online.

As far as performance difference, for the city, a smaller 150 is more nimble. They accelerate just about the same due to weight difference.
The 250's shine when riding with 2 people, on the highway.
On the highway, the 150's peak usually ~60MPH for one person. That's good enough for most people; however if you ever want to go faster you need the extra 100cc's.
Also, if you want to maintain 60MPH (especially with 2 people, or a lot of luggage), get a 250cc.

The 150cc's is good for 2 people cruising 50MPH or below, or a single person upto 60MPH.