Which is the best thermal paste to use on cpu.

Or,

Does anyone have any left over I could have please.

Currently MX4 is probably regarded as the "best" thermal paste. However, MX2, MX3 and Arctic Silver V are usually within a couple of degrees. The MX range has the advantage of being non-conductive.

For fool proof use draw an X with paste across the heat spreader (the metal plate on the top of CPU).

Thank you