If you trade hashrate, then CEX or Scrypt.cc could be profitable. You might also end up profiting if you do dollar cost averaging on Scrypt.cc and things don't get too weird in the market. But the fees on CEX will destroy any long term holding position.

PBMining...well...let's just say I don't really trust them. A 5 year contract is just plain stupid given the rate that hashing power and difficulty increases. You'll be lucky if you make back your principal, and in a year your hashing power won't mean jack. Plus, their numbers don't make sense. After you figure out the cost for maintaining a data center, buying hardware, electricity, etc. then look at what they're charging for contracts there seems to be something missing. A couple other things don't smell right either, but to each their own.

Basically, you're just better off buying BTC directly and holding than any mining contract.