Quinton "Rampage" Jackson for me acjtlslt fulfilled to become a Ufc champion back in 2007 and has notable wins over Chuck Liddell, Igor Vovchanchyn, Dan Henderson, Ricardo Arona, Murilo Bustamante.
His career was already over after his loss against Jon Jones 2011, after 2011 he was not the same fighter but with that said if he went over to heavyweight earlier and with good cardio and right team I am close to say he would be a good contender.
If he had other sparringpartners and team during his Pride career he would have beated Wanderlei by ground and pound and maybe the same with Shogun during the grand prix.
I am however impressed his achievements but do you think he could do more with right team? Let's say he represented American kickboxing acedemy and his main sparring partner was Cain and Daniel Cormier back in 2010?