I'll say forward but TBH I only say that because of how much better Allen got. If you were to tell any one of us back in August that the Bills would finish with more losses and get knocked out a round earlier than 2020 you'd be hard pressed to find anyone calling that a step forward.
However, as I watched Allen, I saw a QB take even more steps towards something truly special, particularly in the last month and a half. He looks to me like a QB who, as long as he's healthy, won't be denied a title for much longer. I would say his progression has been:
2018 - Potential
2019 - Getting better
2020 - Great
2021 - Virtually unstoppable