I agree, start with the Tom Baker episodes. These are the "sweet spot" years of Doctor Who when the writing was much crisper and the props department went into overtime on the sets. Another big plus with the Tom Baker years is seeing some of the best British actors in secondary roles. Some you will recognize, others you'll never forget.
A case in point, I didn't start paying attention to Doctor Who until I saw "Image of the Fendahl". Now I know it's only makeup, but I had never seen giant painted eyes that are only visible when the actor keeps her real eyes closed.
It's low tech yet truly creepy. Also the Fendahl dosen't kill anyone, her giant worm slaves do!
