Many fighters of the ‘base’ classes (M5, M4, and M3, but not M4+ or M3+, for example) have versions (known in-game as variants) with different stats, the idea being that they fulfill a certain sub-role within that class:
- Advanced/Enhanced/Prototype: Available only for certain ships, these are all-around better versions of whichever ship to which the modification is applied. More power, shielding, speed, and maneuverability, albeit not as much of any given aspect compared to the variant dedicated to that particular advantage. Their one drawback, such as it is, is reduced cargo space compared to the baseline ship… sometimes. Depends on the race/ship.
- Explorer (M5 only): Trades off pretty much everything (defense, offense, cargo space) to achieve the maximum speed possible. Explorer variants are the fastest version of the fastest class of ship in the game. That should tell you something. They also inexplicably give you the ability to mount PACs, not that their reduced weapon energy will allow them to use that capability at all.
- Hauler: Ships with this variant tend to, well, be able to haul more cargo than other versions of the ship in question. The trade-off tends to be that they have weaker weapons generators, although they will usually also have slightly better shields and slightly better speed.
- Raider: Meant to quickly run in and harass enemies, Raiders have improved speed compared to their baseline version, being the fastest variants for anything larger than M5. The sacrifice is typically that they possess less shield capacity and a smaller cargo bay, though this is offset by a stronger shield generator. Basically, they’re intended to live up to their name -- they dart in, take a few shots, then run away again, any damage to the shields rapidly recharging due to the more robust shield reactor.
- Sentinel: While it sounds good on paper, Sentinels sacrifice the one thing that fighters have going for them -- speed. While they do have heavier shielding, both the capacity and the recharge aspects of their weapons systems are not similarly improved. This means that, sure, these variants can take a bit more point damage than their counterparts, but once that shield cracks it’s a dead ship because of its comparatively snail-like pace and weak weaponry. (Note that Corvette Sentinels don’t quite have the same drawbacks and benefits).
- Vanguard: The poor man’s Advanced version, Vanguards are typically better across the board than the baseline. They possess a Sentinel’s improved shield recharge rate, better weapon improvements than the Raider, and a general speed increase compared to the base model. The one sacrifice, as with their similar cousins, is in cargo capacity -- which could potentially be crippling if you are a missile lover.