I always liked the original RCT better then RCT2 because RCT1has really interesting level designs
a fan-made mod can be downloaded called OpenRCT2 which adds some great new enhancements to the game, including online multiplayer which is pretty cool (requires copy of RCT2 installed on your computer)
RCTClassic looks really good on mobile (includes RCT1 and RCT2 and all expansions)
RCT3 mobile looks decent except there are no expansions in RCT3 mobile and its probably better with a mouse and larger screen, so I prefer RCT3 on PC with expansion pack Soaked, its my favorite especially if your looking for the most features, rides, and mods to choose from. Its a bit easier than PlanCo and best of all you don't need a top of the line computer to run it smoothly
PlanCo is obviously the best looking, but only if you have a good computer (more is coming so hopefully in time PlanCo will grow)
I would stay away from RCT4Mobile, and stay away from RCT Touch (they are just gimmicks and show that atari doesnt care about the franchise) since all the reviews show that RCTWorld is not very good compared to PlanCo
Some other non-RCT games include Theme Park, Theme Hospital, and No Limits 2
I would say grab the RCTclassic on mobile as its only like $6 and then check out OpenRCT2 if you want multiplayer. But you need RCT3+Soaked to get the full experince of the original trilogy [praise]