I own both of these games, and scythe as well. All three are fantastic, and also extremely different from one another. To be honest, though, both MoM2 and TI4 are somewhat hard sells, due to the difficulty in getting them to the table.
TI4, as you probably know, plays best with 6, though I will say I enjoyed the couple of 3 player sessions I held to familiarize myself with the game. Even at 3 players, though, our games took 4+ hours, and with 6 you're looking at possibly a full day from lunchtime to late evening. It offers an amazing, immersive, highly interactive experience, but most groups would be lucky to get to play it more than once a year.
MoM2 is a game I sort of love and hate. It is unparalleled in offering an immersive horror mystery tabletop experience, but it can be really frustrating in a few ways. In my experience, all scenarios besides the easy beginner ones are extremely punishing. They can feel "unfair" in the first play when you fail because you didn't know what to expect, or even what you should achieve. Then after a 2~4 hour failed attempt, the group is often exhausted and wants to go home. To its credit though, the game is great for hosts who just want to provide a gripping experience for guests with almost no rules explanation. It's one of the best "teach as you play" games I've ever seen.
Both of these games, given the above,are hard for me to reccomend if budget is a concern. In that case I'd easily go for 2 to 3 mid weight games for the same total cost I think. For easy to learn but surprisingly deep space shenanigans, I'd recommend Quantum if you can find it. Cosmic Encounter is a great alternative as well for the politics and negotiation, but you need the kind of group that can revel in the chaos and excitement it brings, even when it feels unfair. For a horror game, I haven't played anything cheaper that beats MoM2, but maybe elder sign or something? I've never played that so I can't say. Aeon's end could work as it is a terrifying, tense and rewarding co-op, though as a deckbuilder it's obviously a very different kind of game.
