In the Tabletop the Answer is obvious. You would choose the Multi-Melta, because that's what a Multi-Melta is for. So why is this so flipped in this? I'm seriously trying to figure out when a Multi-Melta is useful in this... The Plasma Cannon is WAY better, but I still wanted to run With the multi-Melta and compare it to a Standard Boltgun... While the Multi-Melta could certainly take out a ton of weak enemies (Like a flamer... but not as well as a Heavy Flamer...) it was struggling against any thing with Armor.
I cleared the level with my Boltgun because the Multi-Melta Barely made a scratch in a Plague Marine.
Multi-Melta is supposed to be Anti-Armour, so you would think that it should shred a dreadnought. Nope.
Please buff the Multi-Melta. Currently it's like a Weak version of a Heavy Flamer.