You in a mech with any regular standard beam laser of your choice, me as a BA with an AC2. Name the time, name the place.
In my base

Serioulsy, I would choose the distance, too. A spotted BA at 700m is a dead BA. Yesterday a BA was chasing a teammate in a MadCatB, he was helpless somehow. I had SRM4 and dual Gauss and the SRMS would not hit/register. So at one point I decided to go for the big guns. Second Gauss hit him

MG can kill BA, but anything else (except AC20 and LRM) will do a better and faster job.
CheapHammer for example is a BA rape machine with its AC10s, MG and glorious MRMs.