I think the MC251 is like $30 Canadian right now, and the MC1019 is like $40 Canadian (you'd have to look for your own local prices, or maybe find some good deals).
I've got a 251, and it is pretty big, much nicer than the old MC59, but I still have to think about space on it, and be careful not to fill it. And I'm not into some of those huge memory-card-hogging games (well, except for Animal Crossing, but it came with it's own card).
I think if you get a 251, you might find yourself wanting another card sooner or later. So the 1019 is a good deal. Plus you don't have to worry about juggling a number of different cards if you just have one big one.