Unless your vehicle has an odd battery configuration, or is extremely difficult to push, I'd go fairly short and heavy gauge.
Not all vehicles, especially heavier vehicles, jump really easily.
I have had, more than once, to jump a truck... and the car that previously tried to jump it, and now won't start itself.
Heavy gauge cables help. Short cables help. Keeping the jumping vehicles RPM's up helps. Gun for all three.
ETA: The Jeep, and my previous Jeep, jump pretty much anything and don't have a need for long cables. (It won't, however, stay jumped without some RPM's on it fairly immediately) But a car... those often have smaller, weaker batteries, alternators, etc... jumping a full-sized truck, etc, is beyond their capacity and will tend to drain the battery of the jumping vehicle.