126 Votes in Poll
Prawn because of versatility + ability to go in lava lakes (though I do not know how you would get out :D)
They all have their perks and downfalls. The sea moth is great for speed and quick trips. Prawn suit is great all around if you have the extra jet pack and the grappling hook cause you can get out of almost any deep spot. The cyclops while great that it can be a mobile base is tough to navigate a lot of areas due to its immense size. That being said it too is perfect cause you can dock both other vehicles and repair/recharge while in use. It can drain more power when used as a base. Make sure you have tons of power cells and maybe a main base to have your charging systems
I'd go for sea truck