Truly, this has got to be in top three for the Most Frequently Asked Questions.
If attack is the same, Lower stars win. EG. If I have Lehane at 40 attack and you have Tyd at 40 attack, I'd win because of having 2 stars to your 3.
If attack and stars are both the same, attacker wins. EG. If you played Bob Joby to 3 attack with bonus, and I'd play a Spiaghi at the starting pill so I would get 3 attack, You'd win because of going first.