The grip on my kite surf board is peeling off.

What's the best glue for sticking it down?

Also if I end up going down the path of regripping the whole board, what is a good brand to use? It's a classic surfboard shape.

Selleys All Clear sealant; I've used this stuff to glue many things, including EVA foam deck-grip onto kiteboards. Hardest part is cleaning off the previous adhesive which had turned to slime. Being clear, it's good to apply right to the edges, preventing water from forcing its way under the foam.

I used 3M 77 spray recently to re-surface my board. It's been good. It's enough to spray only one side, but it was a bit slow to set. You may need to check it time to time in the next 12 hours.

You can use heat from a hair dryer and then some solvent (e.g. De-Solve-It spray) to scrape off the old glue. Then you can clean the surface with some spirit before applying the new cover.