xperia x10 is better than N8 no argue about that, I use one. but i dont recomend you to buy x10 since never versions has alredy come out of xperia family. go for neo/play or arc
point to be looked at,
1) if ur a tech savy person so for the higher spec and OS (android)
2) if ur interested in the camera 12MP vs 8MP in this case N88888
4)again OS wisely Symbian is a dying OS and android is the best around
5) app core of the android is huge compared to symbian / java
6) if ur used to old customized phone fashion go for N8
Finally when buying a "smart phone" go for Android or Apple