Honestly the basic Helbrute loadout, Multi-melta and Helbrute fist is a good choice because of the Crazed rule.
Crazed: At the end of any phase in which this model suffers any unsaved wounds or mortal wounds, roll a D6. On a roll of 6, this model immediately makes a shooting attack as if it were your Shooting phase if there are no enemies within 1", or piles in and fights as if it were the Fight phase if there are enemies within 1". If there is no visible target within range, nothing happens.
This will save you 50 points for other options (not entirely sure what those could be without knowing what list your going with.) While yes the Twin Lascannon will hit pretty far across the table with 48", I find the Helbrute is a good choice to run up at your opponent with Toughness 7 and 8 wounds.
Comparing weapons the multi-melta has AP -4, which is pretty strong in this edition. The damage between the two weapons is comparable, the multi-melta has a higher chance for more damage once its within 12" (with rolling 2 dice and picking the better number). The Strength of the multi-melta is an 8, (compared to the lascannon's 9), this isn't a huge difference as most vehicle range from 6-7 with Land Raiders being an 8. Meaning more often you'll be rolling 3+ to wound for the most part (4+ against things like the Land Raider or Knight equivalents). Then in melee, the Fist is doing Strength 12 hits, (or spend 52 points for the Helbrute Hammer for the same Strength). Hitting for a set 3 damage at AP -3 and no penalty to hit (-1 penalty with the Hammer.)
That's how I'd go for anti-vehicle Helbrute. Which basically seems to be what these things were designed to go after in their basic loadout.