Here is your Answer. CEX.IO is basically service for people who want an easy start in BITCOIN mining with out the hassle of maintaining hardware. CEX is providing a an online hosted mining service.They sell you there Mh/s that can only be used in there pool (Cloud mining) and they can also be sold to somebody else in there MH/S Exchange.
Whereas BTCGuild is just a simple mining pool on which you use your own hardware to mine BTC.
These days it is foolish to invest in any BTC hardware or cloud mining until you are already rich.
can I have 10 to 12 $ easily after investing nearly 50000 or no because right now I need some source of income thanks
On normal days I earn 10 -15 $ daily and on extra-ordinary days that come very often it goes above 25$ per day including all of the electricity problems. So on average I am earning 18-20 $ daily with 1870 KH/S.
For 50k you will be able to get a 7950 that is capable of mining at 600 KH/S so you would earn approximately 8-9$ excluding downtimes if any.