I would have to spend a few hours contemplating the answer t this one! Since I don't have that amount of time I can't give a definite answer.
I will say it is worth cherishing the few seasons Truly, Clegg, and Compo were together.
Also, I can't put my finger on just one season but approx. 2002-2005 was a good time. I enjoyed being in the company of all the extra's (Enwhistle, Tom, Smiler, Wesley, Eli, etc. Maybe I would select the final years of Wesley and Eli. Towards the latter half of that decade, age finally seemed to catch up with Sallis and Thornton as there roles began to slightly decrease.