One method Tokugawa Ieyasu used to unify Japan and consolidate his power after redistributing conquered lands among the daimyo was to require each daimyo to spend every other year in Edo (now Tokyo). The expense was enormous and the intermittent time away from home worked together to prevent any daimyo from consolidating power of his own.
The saying in Japan is that "Oda Nobunaga pounded the rice cake, Toyotomi baked it, and Tokugawa ate it." Clearly Tokugawa was successful in establishing a long-enduring and expansive shogunate, but his achievements would likely have been impossible without those of his predecessors. At the same time, though, Tokugawa faced plenty of obstacles, and made a number of important decisions, in particular the decision to legally proscribe Christianity, which had been accepted to an extent by his predecessors. The character of Japanese society was markedly different as a result of these and other decisions.
I think the goal of the three unifiers was similar in that they all wanted to establish power over as much territory as they could. It was about gaining control of the contempoary system of power so that they could in turn gain control over the populace. It is always the case that the last individual has the advantage because he or she is able to build upon what has gone before.
Yes, I'd say that Tokugawa was most successful because he was last and was able to build on the successes of Oda and Toyotomi. The three of them were all trying to unite Japan through controlling the imperial court (to give them legitimacy) and then extending their control (either militarily or by negotiation) over as many daimyo as they could.