i went from the mx518 (optical, great mouse) to the g9, a laser mouse
they made a newer version with a higher dpi called g9x though, cant say it really needed it (its also like twice as much $)
the main difference i noticed between the two was i had had a habit of lifting the m518 when turning in fps games and recentering it and you cant lift a laser mouse or itll fuck up your aim, so i dropped that habit pretty quick
another good mouse between the two is the g5
edit: kind of rambling sorry