OK, bear with me here before you unleash.
The usual genestealer brotherhood list is a variant of Imperial Guard with captured equipment etc.
My main problem with this is that even with Straken (who is about the only IG character who makes a passable genestealer) the army will still play and feel like IG and lack that CC bite that you'd expect from stealers. Plus the infantry conversions get repetitive fast.
So how does this look? essentially its henchmen with a few extras to add to the anti-mech potential
HQ
Coteaz = Genestealer magus (must have for this list)
Grey knight characters grand master/librarian (one allowed as the genestealer patriarch/broodlord)
Elites
Assassins = Assassins (not very fluffy, but otherwise this slot would be empty and assassination is a tool used by the cults)
Troops (backbone of the force)
Henchmen:
Arco flagellants = enraged hybrids
Crusader = Corrupted arbites (with riot shields and power mauls/hybrid claws)
Death Cult assassins = Purestrain stealers
Servitors = Heavy weapon hybrids
Psykers = Magus thralls
Acolytes = Genestealer brotherhood
Chimera = looted chimera
Heavy
Land raiders = looted heavy vehicles (again not very fluffy but could work with the right conversions)