I have only rng abused in black and black 2. I can tell you that b1/w1 is rather easy so I suggest you start with that. b2/w2 is a bit more difficult/random. Can't tell you anything about 4th gen RNG, haven't tried that... The easiest is probably if you watch some vids of people doing it, because if you just read text tutorials it might seem pretty confusing (at least it was for me...)