Both are playing off the charts right now, though I think Kyrie is slightly ahead, particularly after the streak he's had in the last 5 games where's he gone over 20pts in each game.
In those last 5 games Kyrie's stats looks like this: 22.6ppg, 5.2 asts, 3.8 tos, 2.2 rebs on 55% shooting, 40% from 3 and 86% from the line, where's he averaging 4.4 FTAs/game.
Besides the A/TO ratio of 1.36, which isn't great but isn't aweful either, his numbers speak for themselves and are pretty outstanding. For the year he's now averaging almost 18ppg, 5asts, 3 rebs and 3tos.
Rubio is averaging 11pts, 8asts, 4.4 rebs and 3tos. Pretty impressive as well, and his 2.5 a/to ratio is outstanding for a rookie PG. (As a note, Rubio is also playing ~4 more minutes per game than Kyrie.)
Overall, Hollinger has Kyrie at a ridiculous 22.41 PER, good for 20th in the league and Rubio at very good 18.5, good for 65th in the league. Here's the full PER rankings list, remember its intentionally curved so that a 15 is the league average. (I know there was a post on this earlier, I was typing this post this morning but never clicked submit...sorry for some redundancy)
Hollinger certainly has Kyrie as is ROY so far (he said so in a column I linked to about a week ago), and has Rubio second. Both should make their fair share of highlight reels throughout the season, but Kyrie's scoring and his team's potential to make the playoffs may give him the lift. Its very, very early, but the Cavs are currently 7th in the east right now ahead of NYC in 8th and Boston in 9th. I expect both NYC and Boston will make a push as we get into the season and the Cavs may dropout, but I wouldn't be shocked to see them sneak in as the 8 seed.