I'd play both and see which one you like. I had both and Johnny is really fast, but it's a basic layout with a glove mechanism that's cool, but the novelty wears off. If you want a fast game, JM is it--there isn't much faster in its price range. LAH is fun with the crane, topper lights, and six ball multiball--certainly more fun for kids and casuals, so if you have guests that wouldn't be into the cyber punk theme of JM, maybe LAH is the better choice. Down the road, it would be easier to trade or sell JM because Williams brand snobs are more numerous than Data East fans.
If they are exactly the same price--JM. If LAH is $500+ cheaper, I'd take LAH and put the extra cash toward the next pin.