Those steel beauties, which are made from around '96 to early 00s, the suspension corrected, V-brake compatible XC frames I like the most. Couldn't care less about newer standards, disc brakes, integrated headsets, wider O.L.D., tapered headtube (or is it fork?), eccentric/ISIS BBs, etc. I'm firmly stuck in the square taper/rim brake universe, period.
The team steel frames of the era in 19" size weigh under the 2 kg mark, some of them are even way lighter but still reliable (if easy to get the tubes dented). True Temper, Tange, Dedaccai, Columbus & Reynolds were at the top of their game back then and I try to keep 1-2 fine specimen made from their high-end steel tube offerings of that period.
In fact, recently I do not buy/keep anything which does not fit these criterias. They're a dying breed anyway, as they won't be recreated (without spending a fortune) due to strict regulations and the lack of availability in decent/NOS condition.