I have never heard a single good thing about Element but I have as of yet to try their stuff.
Modify tends to be good but I have had 3 out of 4 of their pistons I used strip within 500rnds. Their airseal components (nozzle, cylinder head, cylinder, and piston head) are amazing and a lot less than other brands. SystemA airseal components are actually the ones I have had the worst experiences with.
My favorite brand for gears is Prometheus, also tends to be quite expensive. SystemA are okay but are usually over rated and called Godlike when they are only pretty good. I have had very good experiences with HurricanE and have never used Guarder so can't say.