Fantasy Masters - Best (and only) f2p strategic TCG online. It's a good time waster now and again. I still play it. Ranked 79 ;D

DOMO - Only keep this if you can stand the grind.
Seal - Same as DOMO

Angels - I recently picked up this game and so far it's okay. Haven't played enough to give a valid opinion on it though.

Zu - This game lost it's value after the first hour or so. It was okay in the beginning but it just became boring, repetitive, and incredibly easy. If you like it then keep it but I just got bored of it after a while.

Gunz - If you can stand the hackers, the glitches, and the amount of work it takes to get good at it then keep this. Or else get Exteel which, in my opinion, is better and has a more tactical aspect to it.

GrandChase - Haven't played so no opinion on it.