If you're talking about upgrading in general, then ec, if you talking about overall rank in the long run, dn's. Farming makes slightly more than pro parties, but parties are a lot easy since you don't need to time regains.
Farming is quickest. Ecs are best. Unless a 2x/3x promo is going on and you spam dns, then ec is better.
Farming and partying are beneficial. I farmed often, but that's just me. As well as tut trading. Lots and lots of tuts to be found.