...but you don't know the mission, and you aren't sure of the mechs or combined arms you will face. Best tank? Best tank vs. favorite tank? I LOVE the Demolisher- when you get it in the right mission and situation it is beyond beast, but in some setups- like an open field you are in trouble. I accept that in many of my games, I enjoy running my favorite tanks and mechs making things go boom. BUT, if I was going to always put tactics first, and we swing back to the best all around tank in Battletech- my vote?
The Manticore. Speed, armor, weapons AND all around battle value to make it work in any list. We start at long range with the PPC and LRM 10 pack. 10 damage on the PPC has some bite, a LRM 10 pack with good rolling also has some bite, but with the 10 you are subject to a bad spread with a bad roll. If it was a 15/20 less so. But that is two long range tools to fire on the way in either in support of other lance elements or as a main attacking element.
Close range has a SRM 6 and medium laser to bank on, but since it is a vehicle we might as well also fire the PPC and LRM at close or under minimum ranges also- two most likely shots to hit, and two get luck shots to hit. All for 993 (!) battle value.
Which compared to the speed and weapon loadout for a mech, which would be ~1200 BV minimum the Manticore works in any role. EXCEPT where it might come up against infantry, since it has no machine guns or flamers.