I'll exclude Carrick as he's retiring so without him, these would be my personal picks:
Fellaini - Think his contract is expiring at the end of the season, he's been useful but barely had a kick this season due to injury, McTominay has been filling his role in the squad admirably so he'll leave for me.
Smalling - Don't think he's close to being good enough for what we want to achieve personally, he's decent but we've got too much "decent". He can defend 1 on 1 fairly well but he has poor positioning, can't organise a defence or play out of the back. He's got plenty of experience and we could easily get a good fee for him.
Mata - He's likeable but I don't think he's ever really lived up to expectations here, he's often been played out of position and we've struggled to accomodate him. Think he's very symbolic of our struggles post SAF, he was a luxury player who could never quite turn a game on its head consistently. He's very talented but little room to improve in his 30s, at times been a big part of why that right hand side has been so impotent. Simply has to go for me.
Blind - Barely plays but has a lot of ability, think we'd be able to get a half decent fee for him
Darmian - He's nowhere near United standard, can't defend or attack, getting rid is the only logical choice
Too much squad turnover could be very costly at the start of the season, having a settled squad is important to challenge for the League. I wouldn't sell Pogba or DDG under any circumstances for any price. With that said, some (and I emphasise that as maybe 1 or 2 of the following will leave) I could see being sold if the price is right:
Shaw - He hasn't worked out at all here, still young, might have a bit of resale value and we're rumoured to be in the market for a LB. Attitude hasn't been great and always seems to run to the press when things aren't going his way, his injury was a set back and I empathise with him but 2 years on there aren't any excuses now. I'd sell him personally.
Martial - Unhappy with his playing time, he's got a lot of talent but we could potentially get a sizeable fee for him. I'd like him to stay as I think he's one of our most entertaining players, but when he's bad he's really bad. If he starts a game off poorly he very rarely recovers, if he wants to leave I don't think we should stand in his way.
A.Pereira - Left instead of waiting for his chance, whether that's a good call or not remains to be seen, but judging from McTominay's time AP would've been better off staying here. He won't be missed as he was barely a squad player for us.
Jones - Talented but injury prone, could definitely see him being shown the door if we get a good enough replacement in or perhaps promote Tuanzebe instead of signing an alternative.
Herrera - Passionate but very limited, he was great last season in the role Matic is currently playing but Matic is better in nearly every way. He's a bit of a **** hero and seems to give his all on the pitch but he can really be a liability at times.