In Elite:Dangerous, there are different types of vessel hardpoint where equipment can be mounted. These include weapons, utility, bulkheads and equipment mounted internally of the ship.
The amount of upgrades within the game allows the player to customize their ships into their own combat and playing style. You are also able to take a ship like the Eagle and add higher grade equipment like the mirrored surface armour to replace the lightweight bulkheads that normally come with the ship.
From playing Elite II: Frontier a great deal, I found bigger ships might earn more credits, but were a bit boring to play with. So, I just ended up as a bounty hunter/assassin in the most lightweight ship I could find (usually the Falcon/Osprey or Eagle MkIII). Elite: Dangerous also enables you to place this way, although the combat is more fast paced and this is a multi-player game, so you will need to be very competent at combat.