It's a hard task, yeah, and however well thought out one's picks are they're only going to appeal to some people some of the time. I don't recognise many, but of those I do, and for me, Steve Martin as The Doctor definitely doesn't work. His 'silly acting' comes across as to anarchic and intense for The Doctor (I don't think he could do quirks without overselling them), and his serious acting style (which he can certainly do) comes across as too 'husband next door'. That works for the more serious he chooses, but would be too bland for The Doctor. Basically, The Doctor - most particularly now - requires a middle ground Martin isn't capable of.