What is the best thing for a Level 70 member to train on

There are lots of things a member can train on - and they have just about as much things for non-members too. I suggest you go to the Security Stronghold and go to the second-to-last level, which should be the third level and pick any of the rooms in there and train on the monsters there. Bring tons of food so you don't have to make too many trips.

If you're looking for PvP for fun and training, go to Clan Wars to train for melee and Fist of Guthix to train magic (best place because they give you free runes but you don't get to use them after the fight but you get awards and rankings) and Castle Wars for both melee and magic. freaks