I will say this, Jennings is one of the best Jeopardy! players that I've seen, but I think comparing him to Hatten, McKee, Larson, exc. would still be like comparing apples to orangatangs. The formats these legends mastered are comparable sometimes, but still diffrent enough that you can't really compare player A to player B to player M.
And personally, IMHO, I don't think it would be right to toss Dan Avila into the mix of that list, or at least his run on Greed, mainly because he used the assistance of a team of other players to come to a conclusion on an answer, while the other feats previously mentioned were done by one person relying on their own knowledge and only their own knowledge, and perhaps some luck sporadically. (Even though Avila did make the final decision before finalizing an answer.) Most importantly, Avila won jack-squat when he decided to attempt for the $2M, and the same result occured when he lost the $1M MDM. I'm not trying to subtract or undermine what Avila and his team did on Greed, but I don't personally think they can be included in the list of the best GS contestants of all time.
Just my oppinion, though.