Different recoveries definitely have different levels of difficulty.
Actually, I'm a ganon main, but ledge teching was vital to ganon's recovery (his sweetspot sucks), so i learned how to ledge tech. It just happened to carry over to other chars.
From my experience, bowser, DK, falco, fox, ganon, and captain falcon have easier ledge techs. I have the timing off for marth, roy, doctor mario, mario, luigi, samus, and link but i'm pretty sure they just require different timings to be learned.
Well, ledgeteching is simply a great deal more important for some chars like ganon and falco that ppl try to learn it for them. i mean, i'm sure mewtwo can ledge tech like any one else, but there really seems to be little point to master it (although i wonder what a mewtwo ledge tech jump looks like).