Hartnell, Troughton, and Pertwee. Then came the clown who took every ounce of gravitas in the role of the doctor and burned it, ate the ashes, and pooped them into a London fatberg. Also, K9. Oh god, K9. WHY?
Quickly followed by the bystander Doctor who just went to planets, watched the people there get killed off and then would leave for the next snuff show. Colin's was saddled with bi-polar rage and and a clown wardrobe. Despite McCoy's buffonery and the BBC's hatred of the show, the new mysteries of the Doctor's past renewed my interest.
Hartnell - I watched his stores much later on and he's great as a caring yet stern grandfather. A great choice imo.
Troughton - His version was saddled with trying to keep the viewer's interest in a new take on the established character. A very tough job but he did it. His Doctor's hijinks aren't quite my taste but it works as he's not trying to imitate Hartnell.
Pertwee - The first Doctor I actually watched, back when it was on the air on the local NBC affiliate at the end of their broadcast day, before PBS got hold of DW. Stuck on Earth for budget reasons but more action oriented, it was a great hook for me.
Arsehole McGee - Most people's first Doctor. While we got more Sarah Jane and Leela (non cyclops version) we also got a lot of wtf.We got robodog macguffin for those times the writers were overusing the sonic screwdriver. We got to see the Doctor make Romana waste a bunch of her regenerations until she got an appearance that he liked ( a serious wtf to me).
I've met Pertwee and Colin and McCoy and all 3 were charming but Pertwee really made me feel special and important when a young me talked nervously to (in my brain) the first Doctor!
I'd take K-9 any day over Adric, Turlough, Tegan, Mel or Donna Noble...