we visited pompeii last year, beautiful place. we took the cruise ship's tour but i think i would do my own thing next time. train station is very close to entrance and there are loads of english speaking tour guides vying for business. i think this is better because with the organised tour you had to go at everyone elses speed, i am a bit slow, and couldn't linger where you wanted.
bit of a tip though, bring lots of water cos absolutely no shade and the sun is lethal, wear very comfy shoes cos everywhere is cobblestones, and have a look around the cameo factory i got a beautiful cameo necklace as a souvenir.