Well, I haven't played any games recently, but here's my two cents worth.
- Saint Celestine is great.
- Canoness in a shooty squad is a bit meh in my opinion, but if you're running her naked as your HQ choice I guess it's alright. You might want to stick special weapons on the Celestians because they're a cheap way to bulk on meltas.
- Make your sister squads larger if possible, they're pretty flimsy compared to what's running around nowadays. Storm bolters are bad. Heavy Bolters not good on sisters because they can't move and shoot with them. Rhinos if possible - both for protection and mobility.
- Seraphim are okay. Not quite what they used to be, but still strong. Take meltabombs if you still can.
- Repentia at least need some form of transport, Rhino at least. If not they'll get shot to pieces walking before they can get to anything, especially a small squad like that. Once they do, oh boy. But you need some form of delivery.
- Idk about how good Penitent Engines are right now. Low AV walkers with open topped never appealed to me, but I think they've made them tougher since I last tried them.
- Exorcist is always good.