Based on my experience, the payout from PBmining compares very favorably to the amount that I've mined so far using my own equipment at home.
That is in fact why I don't believe PBMining is legit. They payout too well for the difficulty. It isn't a large amount more, but each time I checked they were paying slightly more than they should in theory. That could be luck or it could be they way they wrote code simulating payouts.
For what it is worth, over the last month I've been trading B.Mine at HavelockInvestments. I know that isn't real, it is a virtual mining. However I've still been able to turn 2.25 BTC into 3.11 BTC in less than 4 weeks. The most virtual mining I've held is 970 GH/s. (Daily dividend was 0.029 BTC for 970 GH/s) But I've been trading out when there is a good profit and buying back in when the price is lower. Right now the price is a little high and I'm out.
Anyway the point is why buy contracts when you can't easy trade them and you don't know when the contracts will fail?
(Note: The Havelock site does go down a lot so trading on it is a bit of a pain.)