I know the teams weren't as talented, but I had a lot of fun watching those 2015-2018 C's teams
I also had a ton of fun watching last year's team especially in the 2nd half + postseason
Ultimately if I had to pick, I'd say the Hospital Celtics team in 2017-2018 was the funnest for me especially the postseason. So much fun watching them compete and winning games. Scary Terry, the Jays, Horford, Baynes, etc. Sad end, but to get that far given the circumstances was great too.
Even though 2016-2017 was fun too, I just have some bad memories of it now primarily due to IT's sister, and also the way that ended (IT getting hurt which derailed his career, losing in 5 to CLE with 3 games not even being close; the Wizards series was dynamite though)