My least favorite favors are all the junk we were expected to bring home from incredibly over-the-top bar mitzvahs in my family. I admit to liking the caricature artists, or the photo to take home, but the blow-up guitars, goofy sunglasses, T-shirts in the wrong size with "JOE'S BAR MITZVAH" on them, the singing lobster centerpiece we were begged to take, the candy, the mardi gras beads, etc. ... just too much!
We gave all our guests from out of town "welcome bags" (homemade chocolate cookies, trail mix, candy, pretzels and bottled water with our personalized label on it, plus an itinerary and a map, and a city brochure). The bag was paper with a cute bow and matching label, and there was nothing to take home with you unless you wanted to eat some on the plane. We gave them out as people left our welcome dinner (Friday night, when most people were getting into town).
I have gotten very few favors I felt like were something I'd want to keep around. I like chocolate or something non-personalized, small, and useful, but I do not actually go to an event wanting
Some good, memorable ones: I made little wooden, painted boxes with decoupaged flowers on top and felt liners that family members are still using 18 years later for my one aunt's baby shower.
Another aunt's shower, we painted terra cotta flower pots with daisies, and used them as utensil/napkin holders on the placesettings. Those are still being used on back patios nationwide, 16 years later.