Which one should I use? I want to come as close to the original feeling as possible, but still be able to play in higher resolution. Eye candy is not a must, but some would be cool.

KMQ 2 is all about eye candy, while UP and Yamagi "just" fixes things. But which of the two is the best choice?

I'd say use unofficial patch 3.24 first and see how it goes. If you then want a source port you should still be able to apply one on top of the 3.24 patch.

For me, I use KMQuake2, but as you want something more like the original, Yamagi might be the port you would then need. But definitely try it with just the 3.24 patch first.