I think it would be more fair to say the FWL doesn't have a best trooper 'mech. It has signature machines sure, the Hermes II, the Orion. But 4/6 medium, not any one really. As of FM: FWL the most common FWL regimental makeup was 1 heavy battalion and 2 medium battalions. We see a lot of medium machines.
I think the FWL was meant to represent a mirror image of the DC, which is said to dislike medium 'mechs. The FWL embraced them. But not of 1 specific model like a Centurion or Enforcer. Instead it has a slew of different mediums classes across the spectrum, many of which are more thought of as generic machines common across the Inner Sphere. Or as FWL variants of common machines seen elsewhere.
FWL units often require teamwork because, historically, the individual machines they use aren't that powerful alone. A lance of pure Hermes II would have severe limitations. So would a lance of Hunchbacks. Put a Hermes II, Hunchback, Orion and a Wolverine together and you start to get a sense of what a typical FWL medium lance for much of their history looked like. If you want to lean lighter/faster/more missiles, you can swap out the Hunchback for a Trebuchet, or later eras, an Apollo.
