How to fill the joint between tiles and cabinets in a kitchen backsplash?
I would use white caulk for this, hand-squeezed from the small tubes available at the hardware store. It's flexible enough that it won't crack as the wood cabinets move against the tile, and dries rubbery and impervious to water. Smooth it into the crack with your finger and it'll be nearly invisible. Takes about thirty seconds.

Over time, you'll need to wipe it clean of cooking grease, and it will eventually crack and peel, at which time you can dig it out and reapply it quite easily.