As already mentioned if you get the chance ride both an see how you get on , ive owned multiples of ea cr 125's kx 250's / crf 250's , yzf 450 , crf 450 & currently a yzf 250 im quite happy ridding either i went for the yam yzf this time round because in my experience decent 4 strokes are so much more reliable / easy to start / no mixing fuel up etc , a 2 stoke may well be alot cheaper to fix because the engines are a lot more basic but the 4 strokes last longer imo between engine re builds, both models need proper maintanence though as there race engines at the end of the day and will cost you a small fortune if niglected ... ( im sure you will have plenty of fun which ever you choose


p.s if possible buy the newest bike you can afford and the one thats done the least amount of hours ....