Depends on heaps of factors, age, if you are racing, do you want to get planing earlier, do you want to sail when it gets windier. The 127/9.6 will be easier to use and have a bit more top end. The formula will get planing in less wind and will be a little bit more bottom end.
2014 Starboard W49
2015 Starboard Isonic 87
2016 Starboard Isonic 80, 97,114
2015 Severne Reflex R6 5.6, 6.2, 7.0, 7.8
2016 Severne Reflex R7 8.6