It depends on what you're planning to look at on the walls.
Flat paint, especially in lighter colors (white base) is the best for hiding imperfections. Most of the time, this means poor mud jobs.
Eggshell and semi-gloss paints accentuate mudding flaws in your walls, but are much more resistant to dirt/grease stains and are easier to wipe off. What mudding flaws you see all depends on your lighting setup - where your lights are relative to where you're going to be standing and how it's going to be reflecting off your walls.
I was personally in the eggshell camp for many years. But I have corner lighting in my garage that reflects down the entire length of the wall. This shows ALL of the mudding flaws when walking in through the door. From here is when I decided that flat was the way I needed to go. [Ironically, I had this same issue in a previous home as well, there was a large wall in the living room that you could see down from the kitchen, and when I installed some wall shelves on the opposing wall with backlighting, you could suddenly see the reflectivity of the eggshell down the entire length of that long wavy living room wall from the kitchen; the framers didn't understand the concept of having the crown of the 2x4's all face the same way...].
But unfortunately, yes, flat paint is very sensitive to the lightest dirt/grease stains, even from something as simple from what you think are nearly-clean-gloves; you barely brush a wall (with the back of your glove!) and you see a resulting huge grease mark. Frustrating.
So in the end, in my opinion, it depends on what kinds of flaws you want to see. Mudding/drywall flaws, or future grease flaws.
