Not based there myself but know a few peeps who are and they say you need to be as far up the creek as possible for a good berth otherwise the swell can be a bit lumpy.
Having overnighted at both Haslar and Premier Gosport I’d say Gosport has the edge since the closed the middle entrance on the wave screen a few years back and the shore side facilities are improving year on year at Gosport. Also fairways and berths are wider at Gosport.
Also you may save a few hundred quid with Premier if they are still running the refer a friend discount on the first year. I think it used to save £500.