I STRONGLY STRONGLY reccomend the Wiseco piston (Eric Gorr and Rich Rohrich does too :)). Do the heat cycle break in procedure, and you will be set. Im not sure if this is true, but I have never had a problem. I put 150 hours on one in my KX125. The vertex I had before it shattered the skirt at 60 hours, it was a mess. I hear that the forged aluminum pistons won't break or shatter like the OEM, Vertex, etc. cast pistons. The Wiseco piston is also lighter. One thing to remember though, the piston expands as it heats, so don't beat the bike until it is fully warmed up. Good Luck!
P.S: Do the full top end now, it will cost much less now ($120) than it will when that piston shatters (cost me $600).