A 125 is not the best choice for a trail bike.. I am assuming 2 stroke..
You have to ride it very aggressive all the time since there is no bottom end power.
250F and 250 two strokes are totally different animals.
250f are good trail bikes and easier to ride but IMO 250 2 stroke is way more fun and a lot less $$ if something goes wrong.
A 450 is a lot of bike.. maybe not the best bike to start out on.
Also a 125 frame is usually smaller then a 250 and it feels like a mtn bike in comparison. IT is not much smaller.. in fact you might not be able to tell so good by looking at them, but ride it and you will feel the difference right away.
In the end they are all fun.
