I put a Wiseco pro-lite in mine, I've always had good luck with there pistons. I know there are varying opinions on OEM vs aftermarket, but I just can't see a cast piston being better than a forged one. Anyway, that's the route I chose and, like I said, I've always had good luck with them. Hope this helps.
Pro-x pistons are surplus stock pistons and Vertex pistons are $100 grenades for your engine from what I've heard. I have a Wiseco piston in my 01 CR 250 and havent had any problems. I would use stock but there too expensive and my shop dosen't carry Pro-X so I use Wiseco.