mono block or bi-amps which would you pick?

Mono wins if properly set up. Mono with Pass Labs would be my preference. 

Bdp24... using two stereo amp driving the highs and mid with one amp and the bass with a different amp.  

2 mono amps
 -  being close to the speakers you significantly shorten the distance traveled over speaker wire resulting in less entry points for distortions....AND....
 - since the length is shorter, you can opt for better-sounding speaker wires that may cost more than you'd otherwise be able to afford for long runs from the amp.

I went from stereo to monoblocks and never looked back so, mono it is.

Another vote for monoblocks. I will never go back to stereo again.