Jones was very, very good. We still don't know if he can take punishment from a heavyweight because he simply did not take any. He toyed with Ruiz and his victory was as comprehensive as his victory over Glen Kelly. On that form, he would have to be the best chance of the current crop to defeat Lennox Lewis. I think he would beat Tyson and Tua quite comfortably, provided he didnt walk into the one punch knockout. Tyson's earlyround bustling might be a little difficult to handle (as in Tyson Spinks) but i still think that Jones would beat the current Tyson. The two Klitchsko's and Lewis would be the toughest for Jones to beat. They have the enormous size and reach advantage. In Lewis case in particular, he has a very good jab and boxing skills which could keep Jones Jr at bay, and most likely would. Still, he would have a very good chance but would certainly be the underdog.
As for fighting Ali, if Jones Jr beats Lewis, i think he can be mentioned in the same class as Ali, but I dont think he would surpass him. In many ways his career (heavyweight wise) would be very similar to Gene Tunney's, who retired as heavyweight champion, who is one of the greatest heavyweights, but not the Greatest. To compare with Ali at heavyweight, he would need to beat Lewis and at least 2 or 3 others. Incidentally, if he was ever found to have the chin/heart of Ali, he would raise considerably, imo. At the moment he would struggle to crack the top 100 on the all time list.
I find comparisons to Ali very interesting, Jones's speed is as quick and probably even quicker than Ali's, but can you imagine how easy a pre retirement Muhammed Ali would deal with some of the pretenders in boxing at the moment.