I'd go for Southampton because their FM16 starting squad is probably stronger than the FM17 version will be, so this might be the last chance to quickly succeed with them for a while - and I say that as a Saints fan. The U18 midfielder Callum Slattery is a gem of a player, dubbed "The Next Glenn Hoddle" in-game. Have him tutored by Steven Davis and have central defender Jason McCarthy tutored by Jose Fonte. I gave Slattery his debut as a 16 year-old in my save, then I took him on loan at Sheffield Wednesday and again at Everton in the Championship where he was brilliant, if a bit injury prone. He later moved to Chelsea and then Manchester United.
Success will take longer to achieve at Bournemouth because they don't have the funds. Depends how quickly you get through matches, of course, but if you're going to buy FM17 close to when it comes out then you've only two months to achieve all your footballing ambitions! I'm actually with them now, in season 2025/26, having just taken them back into the Premier League via the Championship Play-Offs. Don't know so much about West Brom.