My current 1G.
I used to run it with an LRM 20, 5 MLs and two AC2. This build is a straight improvement, I cut down on the LRMs due to the tube size but gained a Large Laser. The AC5s really shine as you can pump out lots of DPS with them and you will
cool down while doing so, which matches very well with the laser arsenal.
My current 1S:
A heavy missle boat with BAP and TAG, 40 LRMs per salvo, plenty of ammo, decent close range defense and some long range direct firepower. This is the most relaxed to play, stay in the back of your team and unleash hell onto anything on which you get a steady lock. Or help yourself with the TAG. It is just slow; I recommend cutting the PPC for something smaller and run a bigger engine until you unlock speed tweak.
I broke 1000 dmg with both of these and that was with less optimized builds.
I mastered but sold my 1D because I run better with Mechs that have direct and indiect fire mixed together. But it looked something like
this.
It runs pretty hot so use your agility to get back into cover and cool down. Or simply shoot enemies which cannot shoot back because you outrange them so heavily. Direct fire potential is huge on this one.
In general I agree that Battlemasters do best with high mobility, which means a big engine. They arent really tanky, especially not with an XL Engine, but your agility allows you to use cover and pop out at places which are really uncomfortable for the enemy. Your high torso energy mounts allow you to shot over hills with ease (seriously, they are about cockpit-high) or you can just stick your left arm out for some heavy ballistic fire. The Mech is best played, as others said, a super-heavy skirmisher and a flanker.
Avoid prolonged uncovered firefights because this energy-heavy Mech runs hot at some point. When enemy attention is focused elsewhere, pop out and bring in the pain.
Lastly: New variants of the BLR were recently released. I did not buy them yet, but I did also not see any real reason to do so.