just anything that fits makes me feel better, anything to slow em down a bit is better than nothing. The longer it takes them to figure it out the better. I even take the safety chains when I park it, and with the jack rolled out, I wrap each chain around the jack handle from different directions, and back under the tungue, and put another lock there. It takes less than a minute to lock it down, but increases the time it would take a thief to get it moving by quite a bit.
Probably a good hardened lock is best tho. Actually I'm glad you mentioned that, my better lock was jamming and needed some oil or something, I put a cheaper master lock on it, need to get that better lock back on it. Little cheap locks can be broken pretty easy with a punch and hammer, or a bolt cutter, probly a sawzall too would cut right through a cheap one without much effort.