I'd just pick the cheaper option.
I checked most reviews recommend Crucial M4 256GB over Samsung 840 250GB because of flash chip type. Should I buy Crucial one?
Not just flash type, but also reliability. The m4 is a proven workhorse and very reliable. The 840 has been out for several months, but not for the YEARS that the m4 has been out for. So unless the 840 were much cheaper, I'd go with the m4. But if you don't care about reliability then get whichever is cheaper.
Can GA-Z77M-D3H detects and fits Samsung 840 Pro very well?