Sluggas in Trukks for turn 2 suicide assault goodness, large mobs of shootas on foot for objective holding, firing on softies and
CC specialists, and slowly marching to the enemy's front line where they can mob the survivors.
Large mobs of shootas are great in close combat against non-scary
CC specialists. I'm quite happy to charge a squad of terminators with 20 shoota boyz (with the
PK nob, naturally), and most of the time I come out on top quite happily. Shoota firepower also has a habit of being surprisingly nasty when one doesn't expect it. I fondly remember one occasion where only a single shoota boy was in range of a tactical marine squad. The lad killed two marines
Neither are outright better than the other- they serve different roles, and I sink about an even amount of points between them, and I would be pained to be without either. One may prefer one over the other depending on ones playstyle, though.