In 3025, it's either LRMs or a PPC plus Medium Lasers, with or without an additional specialty weapon of some sort. The LRM or PPC give you stand-off capability, with LRMs offering indirect fire and extended range at the price of needing ammo. The Large Laser and the AC/10 provide decent alternatives for some situations. Once you get in closer, the ML pretty much rules in terms of overall weight/damage/heat efficiency.
Typically, I prefer to have some "specialization" to each design, where they carry a weapon (or ammo) for specific purposes, such as Machineguns, Flamers, AC/2s, Flak ammo, SRMs/Infernos, or anything else with a "niche" role. In a company-sized force, there should be enough of those specialists to cover nearly any contingency.
Once you get into the Clan and post-invasion eras, the addition of double heatsinks and myriads of additional weapon types (Pulse lasers, Streak racks, ER, Ultra, and LBX versions of existing weapons, Plasma weapons, and so on) makes things more complicated, so you need even more variety to cover more potential situations. Generally speaking, I normally prefer one high-heat energy weapon and one low heat ballistic weapon, with plenty of infighting weapons for backup.