You can start it wherever you like. But 3 is heavily related to 1, more so than 2. So I'd really suggest starting at 1. It really makes 3 that much better. Theres a few bosses you won't really get without playing 1. And going directly from 1 to 3 is a pretty great experience. 2 is the best for pvp in my experience nowadays (dont let that make you think its any good its ass a lot of the time). They're all amazing games tho.