I'm on Jerboa and downloaded/installed sync yesterday. As a former RIF user, I don't have a horse in this race. I am more familiar with Jerboa, but find the overall feel of both (admittedly, without a lot of use, to be pretty comparable).

That said, I kind of like some of the ideas in Jerboa more? For example, tap to minimize comments and their children on Jerboa is quite a bit faster. I'm kind of sad that both make selecting some of the text in a comment hard and miss the RIF collapse/expand button. Jerboa also matches the font size of everything else in my UI better than Sync. For example, the font size of this reply and my keyboard are the same in Jerboa. In Sync the in-app font size is quite a bit smaller.

At the end of the day, I think that both apps are going to be largely comparable for a fairly casual user like me. I bet both offer more functionality than I'm using, but so far I don't feel like I'm missing anything.