Best kits, best kits... It's all very subjective. Tamiya does the best engineered kits, but it does not do much for my tastes in modeling... I'd rather sweat blood and guts on any William Bros kits than on any (well, most) Tamiya ones...
So my top ten will include Heller, Sword, William Bros, Revell Germany, ESCI, Trumpeter, Roden, Italeri, Academy and Monogram. But that's without counting garage kits, so I'd have to add, Exokit, MMS, Fine Scale Factory, SHQ, Scale Link, Resicast, Commando5, Rhino Models, AlBy and S&S...
Least interesting, to me, and again it's not always a question of quality... Eduard, Verlinden, Frog, Revell-Germany pre-1990s, AMT/ERTL, Accurate Armour...