How far along are we in to fifth edition? Lackeys of the false emperor date it to over one year and a half ago, yet people are still taking Lascannons on certain units when they should be taking any Melta weaponry their codex has. I shall allow what little command of Mathhammer I have to show what I mean by this. Your Lascannon is str 9, your Multi-Melta str 8, so it looks like the Lascannon is better in range and power. However, that little rule on half distance with Melta weapons makes all the difference, with that weapon penetrating a Land Raider on average. So the Melta needs to be at half range, so what? Mount that thing on a Walker or a Fast unit, and all of a sudden you have a terrifying bubble of rolling on the penetration table, with the final kicker being the +1 on the damage chart the Melta weapon has now for being ap1!
But what about the superior range of the Lascannon, as well as its higher strength? Alright, let's break the Lascannon down. For these purposes I assume Marines shooting. To get a single penetration on a Land Raider, you need six Lascannons to hit it. We will ignore the glance. With Marines firing, that just cost 8 Lascannon shots (33% miss on marines, so eight shots gives you six hits). So to help the odds, let's double that to 16, and call it a day. What statistically takes three Melta-range shots, factored in for accuracy, takes a ridiculous amount of shots from its opponent, and this is with Marines shooting, Dark Gods help you if you're firing with Guardsmen.
In short, stop taking so many Lascannons in your Marine army, take Melta guns! Cheaper, more effective, scary as hell! Heck, I'm updating my Chaos Marines to actually get rid of my two Land Raider transports (because that's all they are for Chaos) because of this, which has only been compounded by the new Tyranid 'dex's Zoanthropes.
Lascannons lose! Good day sir!