Welcome,
I started with SH3 then moved onto SH4 and moved back to SH3, as said before "eye candy" is better in SH4, although that is certainly negated by the Super Mod GWX3 for SH3,
depends on if you want to play the Germans or the U.S. really, (some people steer clear of games that only let you play the Germans).
Personally i think SH3 IS way better, ensure patched to v1.4, install GWX3 and immerse yourself in one of the best (if not the best) WW2 Simulations ever!