I have 100 hours in LC and 50 in ONI. I could probably play ONI for an arbitrary amount of time more, while I'd have a bit of a hard time returning to LC. On the other hand have I enjoyed my time with LC far more than ONI.
ONI is more or less factorio dressed up as a colony sim with some basic chemistry and physics added. LC is a bit harder to pin down. It's a pseudo-puzzle game that shifts focus to a management/RTS game, an easy game that shifts into a really hard game, and a boring game that becomes a really engaging game.
ONI is easy to pinpoint as a Klei game. You are constantly on a knife's edge of survival until you learn it and that aspect becomes a cakewalk and you are instead meant to fuck around. The game also feels a bit shallow in some aspects, or rather the systems seem more involved than they are when you start out.
LC is also very much a PM game. A great story with a lot of subtext and esoteric references, good gameplay that doesn't work for everyone, and being shoddily put together programming wise.
ONI I can recommend if it's on sale. Especially now that they are going with DLC.
LC I'd recommend pirating to try, but if you enjoy it nearly as much as I did then it's worth the current price.