The System can be difficult to learn from if it's your first source. If you have Sybil and OHR under your belt thouroughly, you should have a slightly easier time. I'd probably learn Mary Jane, it looks really fancy and it's not that hard so it's a real confidence booster and makes you feel badass when you pull off the fan flip thing for the first time
Madonna 2 is quite easy along with West Coast Chaos is also an easy one if you'd like something a little simpler, 360 Spider is also rather easy, and is a cool endind for Mary Jane.
I'd stay away from Rev Erdnase, Madonna 1, False Sybil and T.C.T.C.S.A for now as many people have problems with them. Rev E for the weird grip, Madonna 1 for all the pivots, False sybil because of the strange OHR stuff and T.C.T.C.S.A because of the weird palm thing.
So yeah, start off small and work your way up, eventually you'll get them all. Including Pikachu