I'm a big fan of fenders, as they keep me and the bike (including the drivetrain) so much cleaner - and so much better lubricated.

Soooo - enter that into the equation.

How much room do you have in there for tires, and fenders - in my case Planet Bike Hardcore Hybrid Fenders, at 43mm internal width, a few more mm wide externally ( I can measure them if you want me to) cover a 40mm wide tire barely adequately, and are perfect for 32-35mm wide tires.

Plus, they keep the goose poop off my water bottles, and out of my pump innards.