Overall, funny t-shirts sell better. It’s not only my experience. Just recently I watched Michael Essek’s videos where he shares advice on designing and selling and marketing and he said pretty much the same thing. He said about 90% of his t-shirts are funny.
It’s difficult to think of a funny design on the spot. At least for me. So whenever I hear someone says something funny I note it down on my phone or my reMarkable, and then I put it on a t-shirt. It’s one of my habits — collecting snippets that I can later combine, rearrange, and use.