Looking at the kind of ordnance a compact grenade launcher (the kind the Mauser has) can use (Class A, which is only 2X/8A), it seems the Blazer wins with 5E/4. The Blazer Pistol isn't a bad choice either with 5E/3. Against BA, you need AP.
EDIT: Taking a closer look at how armor interacts with AP and BD, it seems to be more complicated. Assuming you have PA(L) with two points of tactical armor, that gives them 6 BAR against energy and 5 BAR against explosives. That means:
The Blazer Rifle will do 5AP - 6 BAR = -1 BD for 3 BD per hit.
The Grenade Launcher will do 2AP - 5 BAR = -3 BD for 5 BD per hit. Area effect AP and BD are reduced by 1 each for each meter of distance between the target and the impact point, which means a near miss of 1 meter would do 3 BD, 2 meters 1 BD, and no damage at 3 meters or more. This also means if you're in close quarters, you'll take damage from your own grenades, not to mention the bulkheads.
So, while the grenade launcher will do more damage per hit, it's much riskier inside a ship. I'd stick with the Blazer Rifle.