TW rules + TO options. Lots of neat tricks available to infantry, and you have to actually plan at least a bit for them instead of smiting entire platoons with your token fire support vehicle, nice for combined arms.
Only disadvantage is that the infantry by themselves are pretty boring. You can run just 'Mechs on the board and it's fun, and you can run just Vees on the board and it's still pretty fun, but just infantry (both conventional and BA) is a bit of a bore. Simplifying all the primary and secondary weapons into 1 range bracket attack and range bracket is not satisfying, and ironically not that simple when playing in person. The quirks of the conventional infantry's construction and combat system don't make for very interesting custom infantry designs, which is important for many of the people I play with (lots of "world builders" in our group).
I had an idea for a rework of that, in which case I'd answer that as the rules I use, but I live a long way away from the rest of the group, so the BT games we play are almost always via Megamek, so no way to actually use them or test them. So in practice, I go with post-TW infantry.
