I personally would recommend the WRM v10. It's a magnetic speedcube that has corner to core magnets as well as magnets in the tracks of the edges that repel the core magnets. Compared to the RS3M v5 ballcore I find the v10 suits me better than the v5.
Honestly, all this hardware can be a bit confusing so if you want a decent cube that's easy to learn on and doesn't have a bajillion combos of tensions, spring settings as well as magnet settings just get a standard rs3m with no spring compression system. Its like 8-9 dollars and easily one of the best feeling cubes you can purchase.
Lubricants are also important, so if you go onto
www.thecubicle.com, you can purchase lubes such as fz calm and rush that will make the cube smoother and faster.
I also recommend getting like a 2x2 if you want to learn a simpler version of a 3x3 cube. The Moyu Weipo wrs is a good choice, or the rs2m evo.