Hey!
What do you think is the hardest genre to programm a game?
And what is the easiest from this 3?

2D RPG(Breath of Fire 2)


2D Space-Shooter(Gradius)


2D Jump&Run(Super Mario)

always ALWAYS depends on the scope

but in general

RPG hardest
SHMUP easiest

when talking about these 3 genres

obviously you can have crazy stuff in a shmup, but standard shmups are pretty much straightforward, thinking thunder force 2 for example.
in jump&runs you have to do more level design and physics

now in RPGs, its whole bunch of stuff
much much level design, enemies, sprites, story & dialog writing
you even have data structures for items and stuff
spells
and then you haven't even started with the battle system yet.

I started creating a top down FF6 style RPG. Then switched to a sidescrolling view (zelda 2) because of less sprite work.
Nowadays it's a sidescrolling action RPG (Castlevania, Metroid, Ninja Gaiden (Nes), Muramasa (Wii)) and I have graphics artists, so it wouldn't matter.

Bottom line: I think there is hardly a more difficult genre to get vast and right, but also the most enjoyable.
Don't start with a RPG or keep it quite simple.

Especially in battle system you CAN use only few sprites and effects (FF1) but you can also have very much, with action based battle systems - Star Ocean 2 comes to mind.