I use React Router. I've had quibbles about some of its API decisions in the past, but on the whole it has served me very well. I'm really excited about the upcoming API in version 4!
In my view, routing isn't a central piece of most React apps, so I wouldn't worry too much about whether your particular routing solution is the absolute best one out there. I will say, though, that the React Router team is smart, hard-working, and committed to solving the community's real world problems.