Long arm in my opinion is ALWAYS better. The long arm kit is, exactly as it says, long arms. The brackets for the arms (which are usually incorporated into a tummey tucker/belly skid for a long arm kit) are moved farther towards the center of the vehicle. They will allow for more articulation and supposedly a ride that feels like stock even when lifted.
Short arm kits are (Don't quote me on this, I may be wrong with the short arm) basically replacements for the factory link arms that are tubular and just stronger really.
For the money, I would definitly go for a long arm kit, preferably the AEV/Nth Degree kit because they are incredibly well engineered and have a bend to them to allow for more ground clearance.
I don't know if you would see much benefit with a long arm kit for what you do, but you can never go wrong with a long arm!