I don't always know if this is the right response, your average mmo player Will be immensely more comfortable with rs3 and it's gameplay mechanics, and this is coming out of a completely
Runescape gold participant who was maxed pre eoc, the reality is that rs3 is a great game in a Great Deal of respects, and much closer to other mmos out there, sure it has mtx but it's absolutely not necessary to triumph the quests are totally killer and the combat can be fun if you're into that kinda thing
If You Would like the runescape you have always imagined in mind, play osrs, it's a bit dated but it's only getting better with a stupidly passionate dev team supporting it that listens to the community and let us them decide what goes into the match, go with osrs, it's a stupidly addictive clicking simulator that will trap you worse than the nastiest of medication habits
If you want a different mmo with one hell of a history that could be described as wow with mtx plus a runescape theme, go with rs3, the Truth is that they both have their areas and audiences who enjoy them, however osrs is definitely the winner between the two to many people, hence why it carries everywhere between 2-5x more players online at any given moment
I'd vouch for one to attempt
Buy Osrs gold, if you don't mind the mill, it's over 2x the playerbase and is not infested with MTX, unlike RS3
Do not get me wrong, there is much more to being a good RS player than having a large cashpile, and a lot of what actually counts can not be bought with gp, but having a large cashpile because you spent like $100 on MTX will surely give you an advantage over players who do not buy MTX, irrespective of which version of the game we are talking about.