As a Roos supporter, my 2c is as follows:
Of the three listed above, I would go Kelly - based on 2 factors:
1) While Higgo is having a great season, he's not a player that will get your 30+ disposals week in week out and smash out some monster scores consistently enough. He is very much a player who will give you 20-25 very good, very effective disposals and score pretty well doing it. Just not at the level of consistency the other two you named might i but that's not to say he won't have equal to or a greater impact than either of them.
2) After knocking Higgo out of the equation, I'd go Kelly every day of the week purely based on the fact that his disposal is first class. Treloar knows how to find it, but half they time while blazing away, he'll turn it over (usually through his kicking). Kelly will be a more consistent scorer (IMO) than Treloar.
In summary, I agree with Rowan - Higgo is a low % play. Go Kelly