There are three primary classes of sub in the game that us uniform throughout each faction: Merchant, combat, and shadow.
Merchant subs are designed to engage in trade, and as a result, boast high hp, and cargo, but sacrifice speed and firepower. Such examples include the Tydeus and the Manticore. The X variants have roughly double the stats such as the Tydeus X, and are competent subs to PvP in, however later in the game, the gimped firepower becomes the sub's undoing.
Combat subs are designed to engage in PvP, and as a result, are somewhat lacking in terms of durability and severely lacking in terms of cargo space, but make up that lost statistic in favor of speed and firepower. Such subs include the Ifrit and the Patron.
Shadow subs attempt to fill the void between merchant subs and combat subs and tend to play a balanced role of trade while maintaining balanced combat ability, durability, and speed. However due to their balanced nature, later in the game, balanced stats tend to be punished rather severely as they do not excel at anything in particular, making these subs an easy kill. These subs include the Omikron and the Tiamat.