I make my own beetle jelly and have experimented quite a lot with both single and multiple fruit blends and I've offered several different ones at the same time to see the preferences
My findings are far from scientific it's just simply my own observations
I also don't use any sugar in my jelly it's just pure fruit/s and juice/s plus several other quality ingredients including one or more protein sources depending what it's for (I don't see the point buying basically sugar saturated jelly for any of my insects even tho they're very popular and beetles love them but it doesn't mean they're good for them I'd rather make my own jelly using only quality ingredients it's the same reasons I make my own Pod and Roach food again with only quality ingredients)
Banana Apple Melon are the most popular single flavours but a blend of all 3 is by far the most popular with all my Beetles and Roaches