Personally, 97-98
I wouldn't mind army building & just getting all the figs & vehicles in multiples
released those years, and I'd be happy.
2002 is a very close second, it had a very very decent Serpentor,
Shock Viper, the Twins, the Crimson Strike Team from the Convention etc
with the obvious exception of the T-Crotch release figures that year
2000 &
2001 were very nice years with all the ARAH Collectors Series