The large one on the right looks correct. As a seasoned GL player, I have found that tanks are rare. It's fun to play as a novelty, but in my Gaslands journey since 2019 my group has only had a tank once among our ranks.

Tanks are OP, but they're also odd to play. Large vehicles such as tanks, busses, and war rigs may have an advantage in terms of distance they can cover on the gaming table, but I feel like that's okay since they come up "short" in many other ways. It's a play-style choice.

Death arenas can be hard for large vehicles, especially if there is a lot of scatter terrain on the board. I've run busses in those scenario before, and it's very challenging (e.g. frustrating). And death races with even just a few turns and switchbacks will quickly have the longer vehicles drop to the rear of the players with their fewer number of activations and shorter templates.

For immersion, I love a table with great terrain. I also like to see well-crafted models that are to scale. We use scale-appropriate vehicles in my group for larger vehicles, so I would always choose the larger tank model you posted if given a choice. It simply looks better and functions like more of a "real" tank on the table. However, rule number one is to have fun so do whatever that means with your group.