Smalling has had one indifferent season at the club, which was last season. He has rarely let United down. He played on the right under Fergie due to the Ferdinand-Vidic partnership, to add height to the team (he occasionally replaced Rafael) and help improve his ability on the ball (this was a tactic used at reserve level during Fergie's later years). His issue under Fergie was his injury record.
For me, Smalling is criminally underrated and is United's best defender. He walks into any team in the league, with the exception of City and Spurs.
Jones has the ability and quality, but he is let down by his injury record. He never had a settled position in the team during his first few years at the club.
As I said in another thread, I disagree with the thought that De Gea is plastering over a lot of cracks. Yes, he has won United points (as did Schmeichel and Van Der Sar) as he's an exceptional goalkeeper, but there's only so much a goalkeeper can do, and there is no way a goalkeeper can cover cracks for three plus seasons. One season, yeah, but three is unrealistic. Did Schmeichel cover the cracks in the Bruce and Pallister partnership?