The problem with what you asked for was you said competitively.
Adepta Sororitas may be the least competitive codex out at this time, so if you are up for a real challenge or didn't really mean truly competitive (like winning tournaments), then Zion's list advice is good.
Typically people take at most 1 unit of Seraphim (usually close to the minimum of 5 where 2 of them have the 2 hand flamers) and then 2-3 dominion squads with MM immolators (most view the flamer versions as shit since you can't move more than 6" and still use the flamer). So:
3 dominion squads with MM immolators, usually with meltaguns but maybe flamers are ok (you could sub in a unit of Seraphim if you like)
rest of list, usually I put just flamer and Heavy Flamer on the troops, for the love of the Emperor do not take power weapons on S3, T3, I3, A1 models.
Also generally I frown on spending +10 points for +1 LD and +1 A.
Wife: "How much do you have invested in these ... miniatures?"
Me: "I don't think invested is the right word."