Phoenix has a faster clear, but Tiger will give you stronger ganks. Also once you start buying items the clear times won't really show a huge difference in times.
I think it's tiger udyr, because he his more adapt to the meta. Tiger udyr makes good early gank, and can be more present on the game. But the phoenix has a good cleaning!
However Udyr has issues with gapclosing and is a relatively weaker jungler out of the mainstream ones.
To adapt a new style people started running Doran's blade tiger udyr for a stronger early game presence.
Tiger Udyr makes Udyr much more fitting in his role as a jungler, but others will argue Phoenix because it has faster clear.
Both work, really, but I'd vouch for tiger for reasons above.