The hardest sights to learn how to use are the open front and rear. You need to line up three things and it's hard for many people to do that consistently, especially when trying to learn how to hold, squeeze and follow-through.
I think the easiest sights to learn on are Red-Dot sights. They don't have much parallax to worry about and there are only two things to line up, the target and the dot. There's no magnification, so you don't see yourself shaking as much as when using a scope. Varying light conditions also don't bother POI like it does with open irons (especially handgun sights, but that's another matter).
The second easiest is a low-powered scope, a 2X or 3X is fine for beginning, so a variable can be nice, but they're more expensive and heavier.
The third option, and a bit harder to learn is the receiver sight and open front. Usually, rifles need to be drilled and tapped for one, and a new front sight is usually needed. This combination is usually more expensive than a cheap scope and/or Red Dot.
Your money; your choice.