On Terminators/Purifiers, take halberds in general. You do not want to have to rely on psychic powers too much, because they can fail you or get shut down.
On GKSS/Interceptors, don't bother with more than a Hammer. Take one Hammer for every 10 power armor guys, and every 5 terminators.
If Falchions are +1A, don't bother, they're too expensive. If they're +2A, then consider them as an alternative to Halberds. They're also the only upgrade other than a Hammer that you might take on GKSS, but only if they're +2A.
Staves should be rare. Don't bother taking them in every squad, only in ones that you expect to get assaulted a lot.