One issue facing any aspiring warboss is whether he should supplement da boyz with big shootas, rokkits, or nothing at all. It very much depends, of course, on who you’ll be going up against—but Glarsnot Bloodcurdle has a few reflections on the matter, based on his own experience.
The conventional wisdom is that Greenskins can’t get enough rokkits. This is certainly the case if you’re up against a lot of light and medium armour, and infantry that AP3 can deal with. I’ve found, however, that too many of my opponents are either fielding their squads in an AV14 Landraider, or have scary uparmoured 2+ Carnifexes. Either way, there’s little reason to be firing rokkits at them, given the remote chance that you’ll hit, wound/penetrate/survive their armour saving throw/do meaningful damage. Indeed, having rokkits might well lead you to slow down your mobs to take pot-shots when you might be better running to close for assault.
I’ve also had some luck with big shootas—the 36″ range and higher rate of fire means that there’s usually a target somewhere that you can do damage to. Plus, of course, they’re a bit cheaper. They especially make sense in shoota boyz mobs, since they same to hurt the same kinds of troops as the rest of the orks in the unit. With rokkits, on the other hand, you’re potentially wasting a lot of shoota dakka every time you use the rokkits to try to take down a Rhino.
Finally, should you be taking the upgrades at all, if your primary purpose is to assault? This is especially true of choppa boyz in an assault-themed list.
I don’t have any hard-and-fast rules about any of this. I do usually take big shootas with shoota Boyz (or, for that matter, in a Trukk mob) for the reason suggested above above. With choppa Boyz, I field them with rokkits if there is likely to be vulnerable armour (and armour saves) deployed on the other side. Otherwise—or, for that matter, if I need the points elsewhere—I sometimes don’t bother upgrading weapons at all. The real armour killer in most mobs is, after all, a PK-equipped Nob.