Since this thread is still active, I'm going to chime in and say that I'm surprised that a few people said they played Cokemon and Bokemob as their first Pokemon hacks.
Both of which, were never very good. But I guess since nobody really dipped into hacking too much and that they were both so crazy-super random and adult themed at the time, that they were hilarious to play.
Both myself and my friend Cat42, created Cokemon (mine) and Bokemob (his.)
I can't remember if I played my friends first or not, but my first rom hack would have to be either my own, or his. =P