My Fanourite Submission has got to be the armbar, for the reason, that most people said, its many variations, I also like the triangle cuz i can get it locked and ready to go quite quickly. This is a little more technical but i like the sort of omaplata with and ankle lock.
Armbars are pretty cool to watch because it doesn't matter how the person is standing/sitting/laying down for it to be applied. I like watching BJJ fighters for that reason, they could be taking elbows to the face and all of a sudden you see the other guy tap out.
Guillotines are nice too, just because they can be applied so early into the fight if both fighters are still on their feet.