I don't think enough good can be said about the 6FC Dragon Fire. I think its overlooked because its not originally a WoB design, and so it gets glossed over when looked at next to the Toyama and White Flame. Its just a solid `Mech. No fancy tricks, no odd combinations (something that you seem to run into alot with WoB designs), just a solid, max armored, 4/6 heavy that overheats by 5 on a running Alpha Strike.
It packs c3i, a Gauss Rifle (with 2 tons of ammo!), a LB10-X (Again, with two tons), 2xERML and an ERLL. It can punch holes in targets while being able to handle vehicles and VTOLs. About the only thing it has a problem with is infantry, and hopefully one of the other 5 units in your Level II is able to handle them.
I'm surprised the White Flame has been mentioned a couple of times, and no one has brought up the D1 Excalibur. 5/8/5, RAC5, twin ERML and a Streak SRM6. Its maybe a bit more optimized for pre-TW play (it has a targeting computer for that RAC), but its relatively accurate, and can fill the heavy scout role that the White Flame does. 3 tons of ammo means its got duration, and the TC lets you hit while jumping around. Though I will admit that it is more expensive in terms of BV, probably C-bills, and has less armor than the White Flame. I've found it useful as a secondary scout, or to make sure that your heavy heavy hitters in the back aren't rushed.