BOGS.Larger sized jumps for sure. You are going to be more patient, and fluid. And it will look cooler.
Looks aren't everything when learning.
Also OP, jump size depends. Idk what you consider small medium and large. Medium as in something maybe 22-32 is good for a lot of stuff.
Gives you enough airtime to perform the trick but is forgiving. When you start you get close to 40 or beyond the jumps get more intimidating for learning tricks.
You don't want to be hucking it on a 5'er with almost no chance of getting the rotation, but you don't want to be blasting off a 45'+ either.
It depends on your comfort zone. Technically a 7 would be easier on a bigger jump(within reason) because you have more airtime. IF you can huck a 5 on a smaller jump, you could hit a bigger jump and do a 7. That said most people get intimidated by the bigger jumps. Some of those people actually spin farther off smaller jumps because they aren't scared and are able to crank out whatever they're trying.
Something you're comfortable with a decent take off and landing that gives you enough air to complete the trick. After that it's all you. Maybe you want to be way up high laying it out, maybe you want to be close to earth. I think 25-30 is a good size to learn most of tricks. You get some airtime and can easily complete them but you aren't crazy high off the ground, and most people are comfortable on jumps that size.