I've never owned a 300 so my first inclination is to say get the 250 as I loved my 99 250EXC. However, having owned 98 and 99 MXC/EXC's, I can tell you that the 98 PDS and fork were not nearly as good as the 99. The 98 PDS really can't be helped dramatically, either. It was internally very reworked year to year.
If I had to make this choice, I'd go with the 300. I've ridden several and they're very fun bikes. Just more lowend than a 250 but yet not the bad vibes of the 380. You'll just have to be a bit more careful with that right hand than you would have to be with a 250.