Interesting. Does it have to be a living thing?
Personally, I'd love to have something like either a Gundam, or those Jet/robot mechs (been so long, can't remember their name) from Robotech. Super stompy power. Rig it for high speed space flight (light speed if possible), & fly to places like Mars or Pluto & just let my destructive side do what it does so well!
If it has to be alive, then I'd say an EVA would be the next best thing. Towering over even a Gundam (Gundam-human larger than finger, EVA-human smaller than bent finger), it would be just so cool! Just a pity you can't get them into space. I mean, they use the bottom of the Space Shuttle as a shield.