I do not have a preference. It all depends on the dynamics. Some characters, like Sarah Jane Smith, Romana, Peri brown, and Donna Noble, worked well as lone companions with their respective Doctors. Adric and Ace did not click well during their solo turns.
Other times, I have enjoyed a larger TARDIS crew. The Ninth Doctor, Rose, and Jack did well together. As did Ten, Martha, and Jack. The ’Journey’s End’ crew pictured above was one of the highlights of the fourth season. I prefer the Eleven/Amy/Rory dynamic currently going now as opposed to just Amy and Eleven.
But I never could really get into the Fifth Doctor’s large entourage, nor did I think Mickey Smith fit in well util his last go around in the TARDIS.
It has to be taken on a case by case basis.
