Best regardless of cost? Or best value, given that its going onto a Disco 1? Or best performance? Or best colour? etc
Personally, I like Alpha Batteries (Google them for website) for keen value, and I squeezed in a bigger one. The standard one is type 072, which is 600CCA. Mine is 800CCA type 334/250. I needed to make another battery locating bracket but no other mods, to get it in.
Nice to have an extra 200 for the winch, etc. Oh, and it has a second set of terminals which made connecting the winch cables much neater.