buy the biggest jumpers you can for a couple reasons...
#1 larger wire, lower resistance.
#2 larger wire, more current. (you'll need more amps to jump larger cars, like trucks...etc...smaller cables wont be able to pass that much current without getting pretty hot)
also make sure the clamp ends are copper. 100% copper. not copper plated steel...not aluminum...a bad connection at the terminal will result in a lot of frustration. you'll definitely have to wait for the dead battery to take a bit of a charge from the donor battery.
you should plan to spend 50 bucks on GOOD jumper cables. 4 gauge jumpers are great. fjc and coleman cable make great cables. parrot connectors will be the best, but the regular aligator clamps are good as well. most important is the teeth material being 100% copper. you want something that can pass 100 amps as a minimum to start a car nearly instantly after connecting them.
(been working on cars my whole life...father owned a garage)