Should I get Roller coaster Tycoon 2 or Roller coaster Tycoon Classic on Steam?

I've recently purchased RCT: Classic on my iPhone because I heard it was better than RCT3; the first game I was exposed to in the series. I love RCT: Classic even more but was wondering, is it worth it to buy it on Steam or just get RCT2 with all of the expansions?

What's the difference between RCT: Classic which combines the two and RCT 2 alone?

Signing out of iCloud / Apple ID. Resetting old iPhone without it affecting my new iPhone?

I'm due to give my boyfriend my old iPhone as his is broken. I need to sign out of the iCloud settings and Apple ID on there but don't know my password for either of these. Some of my contacts have synced from my new phone to my old phone but nothing else has synced eg photos, apps etc. I'm scared that if I sign out of Apple ID on my old phone it will also sign out on my new phone. I turned off iMessage on my old phone, then it notified my new phone that this was tried. If I just factory reset my old phone, will it also reset my new phone as the two are linked?