The reason why I didn't give the priest anything is because without needing the attacks of a character, I can just deny challenges. Also, frag grenades.
Also, the 'Smash' war hymn if you really need it.
Depends if you're holding back as a counterassault unit or going forwards. If you're going to be in the centre of a gun-line, you can't go wrong with the Sacred Banner Of The Order Militant - that area effect attack bonus is just wrong, and whilst you lose one sister's attacks, at +1 attack per model you get an equivalent increase on the rest of the squad.
If using them more aggressively...stic
k with more axes or mauls.
Crusader/assassin pairings are not just the best melee unit in the Adepta Sororitas book but one of the best anywhere.
Essentially, it comes down to what your army needs. A battle conclave is the toughest and killiest melee unit, so aim for that UNLESS:
1) You want a pure sororitas force.
2) You expect to face walkers, monstrous creatures and stuff rocking a 2+ save. In which case repentia. Adepta sororitas armies have a bit of a weakness for monstrous creatures, and they are one of the best monster-shredders in the game, whilst conclaves now (rightly) top out at AP3
3) You want a counter-attack rather than assault unit. If stood in the middle of a gun-line and hoping never to have to fight, then a sororitas command squad is best - not quite as good in a straight fight as the others, but able to actually achieve something prior to the lines meeting. Sacred Standard, Laud Hailer, hell, even a heavy weapon, are options you can throw in without totally losing your assault capability, and boosting up others around you is as valid an option as being good yourself. Multiple priests leading squads with improved reroll-armour-saves-war-hymn actually makes the army not bad at all in assault