pokemon. that's the one that has stuck with me all this time.
though when i was younger i absolutely loved digimon. i never really understood the finer points of it (like the full mechanics of digivolution and stuff) though and i still don't really understand it now, nor do i care to.
my family also used to watch all 3 together lol. except with yu-gi-oh, it was my dad who liked blue eyes white dragon and my older sibling who liked red eyes black dragon. i was a slifer the sky dragon kind of kid