Well, here's my thinking on opfor:
You don't want any free-floaters, because they're either under-equipped, the Proserpina Hussars (been done), the Genyosha (too Stackpole) or Ryoken (not Stackpole enough).
Addendum: is the Amphigean Light Assault group too obscure for your tastes?
You don't want the Otomo because you'll never see them on a border raid.
You don't want the SoL just because.
It sounds like you're in the market for a Regular unit. If so, I can help you narrow down which one. If not, we can reconsider your constraints and plumb the remaining options.