the one that requires a relic right? twin heavy bolter and 2 sponsons. carries termie squads?
for the money i think i'd favor preds and dreads more, but they are intimidating and do have slightly better layouts and damage.
i'm begining to think assault marines are more shock troops than CC specialists.
i think the only economical use for them may be to jump em in to tie up enemy heavies say a hellfire dreadnought or something. run a heavy weapons tac squad in and then let loose and maybe extract the assault marines if they're too beatup. or better yet for chaos use some raptors to tie em up and then charge in the possessed.
hell i find 4 dreadnoughts tend to clean house in general. of course this is generally vs. light opposition. a bunch of assault marines with meltabombs would probably mess up a pure vehicle squad. or use warp spiders with haywires.
I'm kinda disappointed with termie squads myself. they're late game, cost a lot, but don't have the ultra nasty durability they do in minitures, although for standard termies the assault cannons are kinda nice. this is seems particularly true of the assault termies esp. since they supposedly have storm shields.