I was with Bitminter, and after discovering the additional merge mining. I switched to GHash.io.
Only NMC has value, and Bitminter already has it. DVC and IXC nearly has no value, together they add 0.16% extra to your mining income.
0.16% extra income is worth the possibility of 51% attack on Bitcoin?
That should be a hypothetical 51% attack. If some pool does cross that threshold it doesn't mean there will be such an attack. Besides it would be a stupid crime, risk of being caught almost certain and potential gain is probably negative when the costs are factored in. So I would have to disagree ... .16% extra income per week is a HUGE deal. On the other hand there are probably even more advantages of being in a large pool, as you often get to unfairly start working on the new block before other pools do.
=== OFF TOPIC NOW, just my view ===
When it come to fiat currency, identity theft costs billions, but people live with it. I personally think bitcoin would be better off if there was a 51% attack. It would probably survive just fine only shaking out the weak players. After that people would actually have more respect for bitcoin knowing that it is reasonably safe. Anyway, it simply isn't possible to have a complex system without some risks. To me the problems with handling the keys for accessing one's wallets is a vastly larger risk than any 51% attack.