I think that Keyflower scales really well if you like Euro’s. I have played it at all counts and I tend to prefer it with more people. It can be a really mean game in some ways (everything is an auction essentially), but there is a nice spacial element, and a lot of strategy. It also doesn’t take too long, and the rules are very straightforward and well presented in the manual.

If you have the time for it and prefer the opposite then Dune (the reprint of the 1978 game) is best with 6. It is a very social game, nice strategy, and not too fiddly, also can be very mean.