In some respects, hed be good. The highly trained, B. A. Baracus (otherwise known by his actors name, Mr. T.) could definitely be trusted to operate the TARDIS and his background of being wrongly convicted would definitely spur him on to make sure justice was served, as it did in The A Team. However, he has some personality traits that the Doctor wouldnt be as pleased with. Firstly, his bad conduct in the army. How could the Doc trust such a rogue? No matter how talented he is. And then theres his love for violence and weaponry. It seems like B. A. Baracus cant solve a problem without resorting to some form of combat - which wouldnt please the Doctor who prefers to solve problems in much more passive ways. However, hes clearly showed that he doesnt work well in undercover roles both like and unlike those that the Doctor might choose, instead B. A. Baracus confronts his problems head-on and usually solves them in a violent manner. If this doesnt convince the Doctor that this guy isnt the right choice, maybe his name will. Hes not as secretive as the Doctor about his name, B. A. Baracus initials aptly describe his personality: Bad Attitude.