I like working with 11x14 paper for various reasons. My 35mm negatives look 'just right' at 9x12" print area, with a one inch border around it. I also like how my 6x6 negatives look at 8x8" print area.
16x20 paper is sweet to work with, but I start to hit the limits of what my darkroom can produce at that size, and I usually only print something that big when I get a request to do so (not very often). For snapshot stuff I use 8x10 paper and I really like how those small prints feel in my hands.

To me it's important that the print looks good on its own, without being mounted and over-matted. It should be a jewel on its own and a joy to hold and look at. I'm not selling a lot of work, so for me this is a highly personal opinion. If I was able to sell more work, I would not mind getting the equipment to print larger (print washers, tray heaters, and so on). But I will not start printing larger just for me to look at something to enjoy. The expense is just way too high for me to justify on the budget I'm on.

Good luck picking the right size, and have a good time in the darkroom.