Since 1995?
Northey
We were crap from the end of Frawley through Wallace and the start of Hardwick and I don't think any coach would have changed that, but those 1996-2000 seasons were lost years under Walls and Gieschen and anything could have happened with what Northey was putting together. Built in 1994, first crack at the mountain in 1995, then never blossomed.
I see a lot of similarities between the 1995 team and the 2017 team as well--in coaches, workmanlike players, team-first high pressure styles. Northey's ways were becoming redundant as Hafey's had before him, but I reckon Northey could move with the times and get a result with teams in the new era.
He HAD the players, like Hardwick. When Hardwick seemed to have nothing at all in 2010-2012 he always had one thing--he always had the players. That sort of loyalty and man management is key to a great coach. People forget it about Hardwick all too often. In this area he is better than elite he is generational talent. Would Martin have stayed and developed under a different coach to be there on grand final day in 2017, 2019 and 2020? I don't know.