Oh, definitely lipstick. That gets my vote, easily. I especially like red or black, sometimes purple. If I had to pick only one piece of makeup to use and leave off all the rest, the only possibly choice would be lipstick. Actually, I think once or twice I have dressed up and didn’t use any of my other makeup, just the lipstick. 😅
Eyeliner and eyeshadow are also definitely in the conversation. I especially love blues and purples for eyeshadow… and dark black eyeliner, though to be fair that’s the only thing I’ve ever used as far as eyeliner goes! I’ve tried powder and liquid for it, usually like the liquid more for various reasons but powder is quicker and easier to put on and remove. I also have an eyeliner pencil I picked up a while back that I haven’t tried out yet.