To be honest i think that most of assemblies are quite useless
I completely agree, and think many experimented players would, too.
My groups are the following (damn, I wish I kept it short -.-) :
[Must have]
Tactical boots (usually, A-modded)
[Usually assembled]
Hyperblaster Saves time and ammo. just awesome...
Tactical armor (usually, A-modded too, btw)
Nanomachic missile launcher Without any doubts my favourite for nano mods ! I'm sure boots are great, but I already have tacs, and may always hope for phaseshift, anyway)
Cerberus armor Preferably, on a gothic/duelist armor or ballistic vest. assembled doens't implies
worn [Rarely assembled]
Piercing chainsaw, since killing angel of death with non-modded throwing knives is quite boring (and is just ridiculous... I hope that guy has been reworked in 0.9.9.7 :/ )
Tactical shotgun Very cool, but not necessary. (and I always use shotgun. a lot)
Cerberus boots For lava pits...
Power armor Simple and efficient
Biggest fucking gun Not that useful, but so much fun :) And I don't see any real use for F mods, anyway. I usually prefer something else on my hyperblaster.
[Nice but useless]
Tactical rocket launcher Most of the time worse than the (insane) missile launcher
Gatling gun Bullets suck... excellent chaingun, tough. But still a chaingun.
Environemental boots Rather good... but not enough for lava pits, and useless elsewhere.
Elephant gun Really damaging, and great knockback, but ridiculously high reload time. Too dangerous for me, even with shottyman. Not worth 2 P-mods, imo.
Energy gun I would need Fin2 to have the necessary WK. Probably useful for sharpshooters, tough. I guess I'll move it to
rarely assembled once I played one :)
Storm bolter Probably good with an ammo box, which somehow means sharpshooter, again, for me, but I prefer speedloaders so much... I'm sure it's a rather good assembly, tough.
Assault rifle Waste of A mods...
Burst cannon I don't like playing AoMC, wasting ammo, or picking to much EE
All melee assemblies outside piercing chainsaw (or knife ? but the angel could be killed with a blunt throwing spoon... so, why waste mods in it ?)
About
all other assemblies, either too weak compared to normal modded weapons, too expensive, or too restrictive, like stupid cursed armors.
[Special mentions]
Nano-shrapnel (a huge ROFL at losing 5 damages dices at the cost of a
nano mod :) The only time I made one, I finished the game using other weapons, since it wasn't even capable of killing formers...
Nanofiber armor Ruins movespeed AND protection at the same time, at the cost of cool mods O_o
Ripper The only time I assembled one, I got a spear before getting the necessary mods. Also, I lost damages compared to my non-modded chainsaw, since I didn't have enough levels in brute, and ripper's accuracy is laughable. It might be better than a chainsaw for a real melee build, but costs so much for so little benefits...