I preferred David Tennant too. I think his best episode was went he travelled to William Shakespeare's time in an episode called "The Shakespeare Code". I watch it on DVD every now and then. The puns are great.
David Tennant is definitely my favourite doctor, though I did like Christopher Eccleston as well. My favourite episode is the one with the weeping angels.
I liked David Tennant the most out of the recent doctors, but the biggest problem is surely that the episode quality in general seems to have declined recently. David Tennant couldn't have compensated for that on his own.
Unfortunately for Peter Capaldi, his arrival coincided with the plots becoming totally unfathomable. As has already been pointed out, not even Tenant at his best could have made them more understandable. Hopefully, once under the control of Broadchurch/Torchwood writer Chris Chibnall, Dr Who can return to more sensible episodes and maybe show Capaldi in a better light.