I'm building a PC and just was wondering if I should get artic silver, ic diamond, or mx4.
IC Diamond > MX-4 > Silver
I've been using Arctic Silver 5 since I started building really. Have used it on quite a few builds as well as on a GPU or two and my Xbox 360. Works very well. Isn't too stringy and isn't ridiculously expensive.
I do believe AS5 is slightly better than MX-4, but MX-4 has the huge advantage of being non-conductive.
All are good thermal pastes, though.
+1 for non-conductive.
Gelid extreme is the best, I use IC diamond myself but I heard it causes damage on cpus and baseplates so watch out if you go IC diamond!