For us it was undoubtedly Koeman. I actually think Poch is a much better manager but at Saints Koeman pips him. Koeman had to see his best players leave whilst dealing with Schniederlin who wanted to go but wasn't allowed. He then rebuilt the squad and bettered Pochetino's record, whilst getting us into the Europa league group stages.
I also think Adkins achievements are underrated at times. League 1 was a league we should've been getting out of with the squad we had but to get out of the championship at the first time of asking is an exceptional achievement. Most of us were predicting mid table consolidation that season with a promotion push the next year but we smashed it!