Gear 2nd replaced Luffy's regular fighting style and got a lot more exposure, even when something like Gear 3rd was around. Both forms had their utilities and you felt a certain weight when Luffy used them pre timeskip.
Sage Mode wasn't impressive when Jiraiya used it but Naruto was absolutely broken with it. IMO his sage mode moment is much more similar to Gear 4th than it is to the other gears. He proceeds to dominate the strongest character in the series at that point (albeit nerfed) and felt so overwhelming.
What hurts sage mode is the fact it's rarely used after this and Kyuubi Chakra Mode (and later Bijuu mode,) are simply better than Sage Mode. It can give Naruto a different type of chakra, durability and better sensing, but Kyuubi Chakra Mode gives him better chakra, more of it, makes him the fastest shinobi in the Alliance... And this comes 77 chapters after Naruto uses sage mode for the first time.
So I think I'd go with gear 2nd. It was better utilized in the manga up until Gear 4th was a thing.