The argument between Bo3 All Gens and Bo3 SS barely matters in my opinion. The Bo3 slot is gonna be filled up by either a) your strong tournaments player (see: Finch, Lunala, whoever else we trick into signing up) or b) your best CAP main (D2, Darek, Rabia etc). The former category will be simply passed teams because that's basically what you they signed up for, while the latter shouldn't have an issue with building for a CAP metagame they mostly know. I realise that the three generations aren't exactly the same and there is obviously different skill sets and player tendencies that make you better or worse between generations, hence why in OU you hear mostly of people maining a genereration rather than a tier. However, I sincerely think that picking Bo3 all gens is a better idea because it makes sure your old gens players are gonna be able to test with the bo3 slot and they both get experience in both the metagame and match-ups that way. If you go for Bo3 SS + 1 ORAS slot, the ORAS player is very likely to be left completely alone and only be able to challenge the manager(s), wheras with 3 SS / 1 SM / 1 ORAS / 1 Bo3 All Gens you avoid this issue.