I'd go with the following H/M/M/L combination, for a FWL flavor:
ON-1K Orion (base model, decent balance of long and short-ranged firepower, tons of armor) (Alternate = TDR-5S)
HBK-4J "Swayback" (2XLRM-10 version, with 5 MLs if anyone gets the stupid idea of closing) (Alternate = WTH-1)
HER-2M Hermes "Mercury" (7/11 speed and decent armor/firepower mix, perfect "backstabber") (Alternate = PXH-1)
FS-9M Firestarter "Mirage" (jumper, another good infighter) (Alternate = JR-7F)
I've fielded this combination many times in Megamek, with consistently good results. With the ON and HBK serving as the "anvil", the combination of jumpable and faster ground-bound elements are generally able to quickly demolish any opposing skirmishers in almost any terrain, then outflank the opposing heavy element. As the opposing units start engaging the "anvil", the mobile "hammer" pair closes in for backshots or physicals. Both have Flamers to add insult to injury if the opponent over-fires and gets toasty, and MGs to exploit any armor breaches that are made, or remove pesky footsloggers that get in the way.
The unit is a bit LRM-heavy, and ammo dependent because of that, but nothing else gets the job done as well for the tonnage and heat. As long as you're aware of it, and stock up sufficent LRM ammo in advance, there should be few serious problems. The ON is unlikely to run out of SRMs in several back-to-back engagements, but it would definitely pay to bring a few extra AC/10 rounds for an extended campaign. MG ammo isn't even worth thinking about, other than having too much on board at any given time (although I've actually managed to burn through about 30 rounds in a game with the HER before).