I really like both.
Ibiza Rocks Diner has the same food as the bar in San An, so think good value, big portions and some really tasty Rocks ribs! Nice big TV for the sports etc and usually got some live music / DJ.
Plastik Beach is also great, very laid back, strong and tasty cocktails and the food menu is also very good. Lots of deals (Free cocktails / shots) etc and they seem to be throwing a good few parties there. Overall not very busy but the people that go there all seem great so it more than makes up for it.