First of all; all the info is here:
https://www.underrail.com/wiki/index.php?title=Jet_SkiThere are five categories of jets: junk, military, melee/speed, hybrids, ranged/defense
junk: junk jet, scrapper, scooter, skimmer, freighter, reef glider
military: aegis patroller, protectorate cruiser
melee/speed: blazer, phaser, torpedo
hybrids: glow, shark
ranged/defense: plasma leviator, devastator
The junk jets are garbage; they get you from point A to point B, slowly, and without style (except the reef glider I guess). They're cheap though.
The freighter is for Al Fabet-ing and another reason that I won't spoil; it's also very protective for it's price (14k).
The military jets are "free" (meaning you can steal them/kill for them if you don't mind faction hostility) and one can be given to you in one situation. They are slower/less maneuverable than the hybrids, but tankier. Perfectly suitable for ranged characters, but not specialized at it (or anything for that matter). The patroller is slightly more maneuverable, but slightly less tanky; they are almost the same.
The melee/speed jets are the fastest and best for offensive melee characters. The torpedo is the fastest (by quite a bit) and most maneuverable in the game, but also the worst for ranged combat and also the least protective and most fragile. The phaser is the 2nd fastest, but is somewhat tankier than the torpedo. The phaser is the cheapest of the non-junk jets (16k, blazer 17k, torpedo 22k) and is equal to or better than the blazer in every way, except it glows (green) and thus makes you easier to hit with ranged weapons and ruins the ambush feat (if you have it). If you just want to go fast (in style) and dont care about anything else, get the phaser.
All three of these have turbo; turbo makes your jet faster for two turns but uses up more battery power; the faster your jet, the more damage your melee attacks deal.
Jet ski combat favors ranged attacks, due to the fact that you can't target land enemies in melee unless you and they are right on the edge of the water, so for melee you are generally limited to sea serpents and other jetskis.
The hybrids are the best jets if you are both melee and ranged, and are the most stylish imo. They are middle of the road; faster/more maneuverable than the military jets but less tanky. They both have built-in ranged options; the glow can shoot lasers (and has a larger battery for this), while the shark can shoot rockets (like mk6-7 HEs with a radius the same size as plasma grenades; note it costs 30 action points so you can shoot a rocket and throw a grenade on the same turn) though the rockets are fairly heavy and will slow you down. The glow glows (red), same as the phaser, and is the 2nd most expensive jet (29k; shark is 25k). The glow and the shark are otherwise almost the same as each other; the glow is slightly faster but less tanky (though it has better energy defense). Note: the shark has a larger engine capacity (which could potentially make it faster than the glow, I think, but with the rockets probably not; haven't tested it).
The ranged/defense jets are the best if you want defense and/or a good platform to shoot from. The leviator is the 3rd most expensive jet (28k) and the devastator is by far the most expensive (42k; 13k more than the glow). The devastator is the tankiest jet in the game and has the most powerful built-in weapon (it's basically a naga blast that costs 50 action points). The leviator has a built-in plasma cannon (like a plasma pistol), and is slightly faster/more maneuverable, the 2nd tankiest (but the best energy defense); perhaps the best choice for gunners.
Note that while out on the water, you are in the darkness and can often trigger ambush on land targets.
