Runescape > Maplestory > SRO.
I've played all 3, and Runescape is pretty far ahead in terms of overall gameplay. Maplestory is a good game on its own rights, and silkroad is just bad.
Runescape has a VERY good and caring staff, despite what people say. They care about the game and the rules and such, and there are many updates, a lot of which are focused on new players. There are lots of various things to do in Runescape.
Maplestory is a good game, however it is extremely tough to get far in the game and levelling up gets veryyy boring. Unlike runescape, its more customizable and such, just very repetitive.
Silkroad is a TOTAL PIECE OF SHIT. 99% of any character you see ingame is a bot, has botted, will be botting. The game makers do not care, and the game just sucks. Do not play it.