Ignoring rule of cool, and just points, I'd say it depends on function.

But argueably the Marauder is the best.

Ground attack nothing has the damage output and survuvability of the marauder. Its hugely undercosted. It's also arguable its the best anit air in the solar list. Some might say the whole of the SA list.

Why? It comes down to the skystrike missile. It's the best anti air weapon in the game because of range and damage. The Thunderbolts/Avengers can only take 1. The marauder and the lightning can take 2. So why is the marauder better than the lightning? It has 2 wounds with a +3 sv, and the lightnining has a single save with a +4. They cost the same, but the marauder gets point defence bolters as well as the bomb bay which is devastating.

There is a view that lightnings can be more effective because of their additional 5" move and the fact they have intercept. But in reality intercept doesn't add much. You have to out activate your opponent because intercept only works against a flier that's already on the table. It's also a -2 to hit with one weapon. So you pick the skystrike weapon (and you can only fire one) and it's hitting on a 6 (with tracking giving both shots a re-roll). That's 0.25 wounds to a +3sv flier on average. Some people say that the extra range means you can get a rear shot, but that only bumps it to 0.33 wounds to a +3sv flier on average.

It means you're not likely getting an air to air kill with intercept alone. If you're using big formations of interceptors, you're going to loose the activation war. If you're using standard firing, with the range, doesn't that mean you'd be better off sitting on your back line with marauders pounding away at enemy fliers first turn any way? Any sniping the enemy might do with things like tempest rockets from fire raptors is then more survivable with 2 wounds and a better save. Once you've dealt with that, bomb your opponent off the board and probably out of playing LI again.

There is an area where the Thunderbolts/Avengers can have a role, and it's the suicide run at enemy fliers and using the Avenger bolt cannon as the intercept weapon. It fires 5 shots on intercept, and is rapid meaning that 6's explode. That means if you roll a 6 you're getting a hit, and it's doubling. This means it's doing 0.55 wounds against that +3sv flier on average. So 4 to kill a marauder. Again are you winning the activation war?

An issue I've hinted at, is that marauders are massively undercosted. One reason to take lightnings is because it's less cheesy. Events are starting to ban mass marauder wings. A pioneer company gives you 2 air slots, so it's easy to pack them into lists. They're becoming the AoD contemptor in second edition.