Good question. I think that the McCoy era was sadly the only one that ended better. Its start was utter shit (sorry Maxil, but it was, utter shit.) The ending however was one of the best eras of the shows history.
Davison's era meanwhile probably stayed the same overall throughout. There were some awful clunkers in his last year, but also his greatest stories with Caves and Resurrection. These probably balance out his average second season.
Troughton meanwhile its a bit harder to say. Some of his best stories are in his first year, whilst some of his worst are in his last. (Though there are some classics in his last year, like The Invasion and The War Games.)
Still during his first year, Troughton is a bit more unsure in the role. He's a bit of a Hartnell light, where as obviously by his third season he's got the character down perfectly.
All of the other Doctors meanwhile I think had reached a fairly natural end by the their time in the role, except for Colin who could have done more, but his second season was hampered by executive meddling, behind the scenes drama, and poor creative decisions from Saward.