between those choices 250wx2 WITHOUT QUESTION if you are planning on mostly sps. After having 175w x2 on a 20" tall tank and now 150wx2 on a 16" tall 3ft 30g both with sps I wouldn't recommend 150w for anything but nano cubes unless you are going to use lumenmax 3, cayman sun or other high performance pedants. I had 175 Aqualine 13k over a 20" tank (same height as a standard 75g) and all sps grew like weeds. SE 175w with decent bulbs are WAY superior to like quality reflected and (required) glass sheilded DE 150w set up but even with the 175w and the quick growth and good color I wanted 250w.
and obviously 150w will grow sps and there are plenty of examples and I grow sps fine as well with 150w. that in no way changes the fact its far inferior to a 250w x2 set up. ask almost anyone that doesn't have a nano cube thats predominantly sps with 150w and 8 out of 10 will tell you they wish or the plan on upgrading at some point. better yet ask somebody who's had both 150w and 250w and see what they say about the difference in results.