Which Ratchet and Clank?

I have seen people recomending ratchet and clank numerous times in this subreddit so I decided to try it out but as I searched in amazon I found at least 4 different R&C games. So, which one is the best? where should I start? Is there one I should avoid? All advice towards this will be greatly appreciated

EDIT: Thanks everyone for your great answers. I do have an old PS2 lying around so when I have a chance I'll get the ps2 games but right now I have cash only for one game so I'll get a Crack in time as it is the more reccomended. Thanks again!