To add some depth to my earlier comments about custom designs, I'll give some examples.
Hellstar or Warhawk C->
Daggerstar. Natasha's Daggerstar is a near-strict upgrade adding an interface cockpit and a targeting computer at the cost of a heatsink. The improved targeting is devastating enabling things like central torso aimed shots or called shot[high] at long range. The lost heat sink is a negligible concern if you are using tacops rules where you could link 2 ERPPCs to heat sinks or dialdown an ERPPC.
Bane 3 or Mastodon->
Greatbow. 16 Streak-5s puts more expected missiles on target than a Bane 3 and it has about twice the armor. The CLPS and Angel ECM enhance the defense even further allowing duel with a Mastodon. You miss out on specialty munitions of the Bane and there are a few situations where the extra range of ERPPCs or ERLLs matter. Note though that ERPPC, ERLL, and LRM all have the same extreme range bracket.
Executioner F or Jade Phoenix->
Greathawk. A Jade Phoenix style assault skirmisher except with a jump of 7 instead of 5 and 3xLPLs instead of 2x ERPPC+HAG30, targeting computer, an interface cockpit, and a CLPS for a massive targeting advantage. It floats along at long range bringing in devastatingly accurate fire while being extraordinarily difficult to hit.
Dire Wolf ->
Great Wolf. An omni assault with Ferro-Lamellor, Reinforced IS, and Void Sig while sporting an interface cockpit. It has modestly less pod space than the Dire Wolf but still adequate for quad long range weapons and the defensive enhancements provide much greater survivability at all ranges.
I'd also add Natasha's
Ghost Bear. The Ghost Bear uses TSM+Supercharger for a run 10 close assault. The claws on the hands deal twin 28 point hits puncturing all but the toughest armor, and then the 5xSRM-4s shred exposed structure. It also has ERPPC+ERLL for sniping at range or in closing. This is sure to be a priority target on the battlefield.
The last thing that I'd note is that direct fire artillery is rarely used but a devastating equalizer. You eat a +4 penalty and have a minimum range of 6, but you ignore TMM or stealth and many forms of cover. The specialty munitions are great. Using cluster rounds on an Arrow IV you use the strike from above table. Using Inferno rounds you can threaten many mechs with overheat lockup. Using Air defense arrows you can direct fire on airborne units with a range measured in boards. An IS variant of this idea is the
Headhunter.