Rollercoaster Tycoon or Rollercoaster Tycoon 2?

First is best but second has more stuff in it

second is like the first, only better

I have fonder memories of the second, though both are pretty good and compareable in quality.
They are also by far better than RCT 3 in all but graphics.

It'll remain to be seen how the new game will turn out.

I would personally go for the first one because I preferred it. But RCT 2 has more content and can be modded to add even more goodies.
Or you can just go with the first one, beat it to death and go with RCT 2. :D

I only played the 1st one, one of my childhood games. It's still great even to this day :)
2nd one looks the same but with more stuff.

I played so much of the first one that I would highly recommend it if it weren't for the fact that RCT2 looks even sweeter.

I would recommend the second on because of Open RCT2. This allows you to have a sandbox mode, insane roller coaster speeds, and other cheats. Also, it has a multiplayer feature that works a lot better than I would have thought. https://openrct2.org/

Get both
Download OpenRCT2
???
Profit