1.) PS2 (Hands down. Mine is still used on occasion to play the old classics.)
2.) PS3 (After the long run, I put it above the PS1. It gets more use than my PS2.)
3.) PS1
4.) PSP/PSVita (Honestly, I think they are comparable for what they ultimately offered, one just wasn't a flop.)
6.) PS4 (Nothing of Note ---> Bloodbourne ---> Nothing of Note.)