Meltagun: 20m s/-/- 2d10+10e 12pen 5clip 2full
Special: Melta; At short range, this weapon has 24pen.

Plasma Gun: 90m s/2/- 1d10+8e 10pen 20clip 5full
Special: Maximal; Maximal mode gives this gun 100m, adds 1d10 to its damage, and awards 12 penetration. The weapon must recharge for one round after being fired on maximal mode, and uses 3 times the amount of ammo per maximal shot.

Special: Overheat; On a roll of 91 or higher, this weapon overheats, the wielder suffers a single hit to his arm, and must pass an agility test of drop the weapon. The weapon must then spend the round cooling and cannot be used.

So, which should I roll with? All factors included, even attachments.

Melta seems to be for taking away their METAL BAWKSES, plasma for killing heavy infantry.

Are you happier killing big angry things at around 400m or at 100m... and hope you don't miss much? If you're going to be fighting armoured vehicles or their equivalent organic friends on such a regular basis, you might want to question why your GM is being so mean to you, chances are its because you've got a melta gun and thus equipped to deal with such eventualities

Being a big fan of Melta weapons in TT(Guard army w/every specialist a melta, vehicles with meltas etc) and the RPGs (rogue trader with digital meltas, AM with wrist mounted melta(s), Explorator with Multi-Melta, Marine with Meltas and multimeltas etc )I would say go melta.

For close, nitty gritty combat you want to make sure the target is dead. Are you fighting a guardsmen, a marine, a tank? Guess what, they are all essentially a womp rat that you can take potshots at in your t-16. Want to get through that dreadnaughts armour? That pesky and nosey Inquistor neighbour happen to get his newspaper in his full heavy power armour? Problem solved.

Just don't miss. There are lots of powerfull weapons for long rang, but nothing compares to the stopping and penetrating power of a melta at close range. Turns the smallest and weakest of scum into an Astartes bbq'er.