Is it really fair to advance Aristotle as the "scientific method" candidate? His writing proceeds logically, but it's not like he adopted the party platform of enlightenment empirical rationalism. If you tend to vote against "faith" or "unscientific religion," I request the formality of a bias check. Are you biased against Jesus because he doesn't look scienc-ey enough?
The Aristotle vs. Jesus question is a worthy match, and it'd be wrong to dismiss either. Both shaped the growth of western civilization in irreversible ways. Scholastic theologians in the middle ages worked pretty hard to reconcile the teaching and worldviews of both, and the results weren't as biased towards the son of God as you'd think--it has to do with the subject matter of their teaching. Are you interested learning to be a statesman or writing laws? Read Aristotle. Interested in God, the afterlife, what to do when you're not perfect? Read the scriptures (i.e., the teachings of Jesus as recorded in the gospels).
How are we measuring greatness?
If we're talking about each's influence on civilization ...whoof. It's pretty hard to tell. Is it fair to credit Jesus with everything that Christianity did for western civilization? Inasmuch as Christianity is "Christian" and based on what Jesus said, I think so, but it's a really broad category. Aristotle's influence is somewhat as far reaching in terms of the preservation and study of his writing, but the Alexandrine school of philosophy hasn't had the same sort of lasting institutional durability. If you're conversant in Aristotle's ideas, that tends to be the result of higher education, rather than a cultural osmosis.
If it's in terms of "numbers of followers," I'd hazard a guess that more people alive today think that Jesus is the incarnate son of God than can name three things that Aristotle wrote without having to google it. Use a different metric (one which categorically excludes any sort of religious claim before starting), and of course Aristotle is the attractive choice. But that's cheating.
Here's one contribution Jesus gave to western civ: Monotheism. One God for everyone. The jews were monotheists before the Jesus walked the earth, sure, but Yahweh tended to only be the god of the Jews. Jesus consistently taught that the promises of God, from the time of the old testament to his own time to after his time... all of these could be applied to all people. You didn't have to be born jewish, get circumcised, or live in Israel to have Jesus as your God. That's one of the reasons the greco-roman world COULD unite behind christianity--Jesus' life and teaching (and death and resurrection, mind) gave an understanding of the relationship between god and man which transcended race or tribe or nationality.
TL;DR: Jesus, because the west united in his name for 1900+ years.