having only been on mike ball a few years ago now, I can only comment on the research I did between the two myself.
the only difference I could find was that MB is a cat, SoF is a single hull, which makes for less roll on MB but more up down movement. not sure which is worse? I was on the top bunk up the front of MB (the cheapest beds on the boat) and quite literally hit the roof on one occassion when we had a very rough night. I'm not sure how often they get big seas.
the quality of service seems to be the same on both, they feed you at every opportunity with delicious food and take great care of you. I quite honestly was at the point of flipping a coin to go with one operator (MB may have been margionally cheaper, but less than $80, which is almost irrevelent) I recall the tipping point for me was the flights that connected with MB were cheaper, so I went with them.
again, from the research I completed, you would have to be an almost impossible customer to be dissatisfied with either operator. both dive operations sound very similar in their approach, both have EAN, both have guides. the briefings on MB were outstanding and probably the best I've received, there certainly was no "reef on the right, fish on the left... pool's open..." edit: but also not a 15min of rambling, which is even more important I think in dive briefs.