Both have a hardening effect, but Primo is generally considered to give less size but more maintainable results. Also Primo is easier on the body, and can be run for a long time with bloodwork not really being affected for most people.
EQ will give slightly more size, some might compare it to Deca. The main difference is that you can get by with 600mg EQ and its not as faked. Primo you really need 800mg to hit the sweet spot, and you already know it can be bunk quite often. EQ can have a negative affect on blood viscosity... last summer my uncles blood was really thick after only 2 months...
I love Primo and ran it the last 3 summers, this year im just doing EQ to save money.