It depends on your game logic but I would say: neither!
Your game should see the players as Mechs and the bots as Mechs, and deal with Mechs accordingly. If your bots see an enemy Mech, what's it matter whether it's a player or a bot? Shoot it!
Your game should differentiate between a Mech who's a player and a Mech who's a bot only when it's necessary - otherwise it shouldn't really need to care! Same with differentiating between a Mech who's on one side and a Mech who's on another.
This could tie into component oriented design where your Mechs might be similar entities but one might just happen to have a player control component and another has an AI control component - it would circumvent any inheritance issues.
Note: Mechs and Mecha are a similar thing with two very different design ideologies and I know the question states Mecha but I've just gone with the Mech term in this answer