Dr. Leonard H. McCoy. He's a doctor not a bricklayer. He knows when a Murderer and Assassin and has an eye for dramatic arts. Count on him! :P
For me it's between McCoy and The Doctor. McCoy was the relentlessly humanist counterpoint to Spock, the Doctor single-handedly made a series watchable. Nothing against Crusher or Bashir of course. Crusher was emotionally uncompromising in protecting human life. And Bashir...well, there are two Bashirs, loveable pervert and genetic genius. I give them both a B-.
I voted for Bashir, mainly because I couldn't stand him early on and then he grew to be one of my favorite characters on the show (could have done without the genetic engineering angle though) But will always think Mccoy was great as well.
Bashir, no contest for me. Though I love the holographic doc for his hilarious pomposity and his attempts to turn himself into an individual.
Bashir and the EMH. Whilst this represents the Siddig's and Picardo's acting abilities, you can just sense each character's dedication to their patients' wellbeing, and going above and beyond the call of duty to do so.