They are pretty much completely different games. Mapleroyals has a very large user base for a pre-bb low rate. If you like to grind levels and play old school maple, Mapleroyals is the best choice.
If you want a slightly faster rate (16x instead of 4x) and an easier time making good gear, Maple Destiny is very good too (They did a wipe in February so the market is fresh).
I do not like current maplestory at all, so I know little about Ellinia. In my opinion, if you are going to play Ellinia, you might as well play the reboot.