I still have one more First Doctor serial to finish (The Edge of Destruction), before I finish up my "Beginnings" set. After that I have three options (probably a lot more, but I limited it to three). I'll either pick up "The Three Doctors," "The Twin Dilemma" or continue on with my Seven watching with "The Happiness Patrol"
I'm actually leaning towards "The Twin Dilemma," just because my only exposure to Six as of right now is seeing him for the second or two he popped up after Five regenerated into him. I know he has a bit of a reputation, but I want to give him a shot before forming my own opinion of him.