It's in a mixed-match relationship with the La-7.
Slightly more maneuverability and less speed - Yak-9U
Slightly more speed and less maneuverability - La-7
You can disregard Ack, since no plane ever seems to bother his P-38L at all.

Not much of an analogy, and not much of a help as well.

As for the most of us average grade virtual pilots who constitute the majority of AH world, teh Yak-9U is a very fine machine which belongs in the same class as the Bf109G-10, Fw190D-9, La-7, and the P-51D. Since the element of success for average pilots in the MA is speed(to run away at the first sight of disavantage), the Yak-9U has speed enough. The fore-mentioned planes are about only ones that will catch it, and they are all outmaneuvered by it.
Ofcourse, when you get caught in a mixed match of Las and N1Ks or Spits, you're dead - but that's same with any plane any pilot, so not much of an issue. Concerning 1944 standards, it is one of the best planes with superb balance between speed and maneuverability. As a one vs one machine, it is also deadly lethal.
Among the faster planes, only the G-10 and the La-7 are pretty much a contest in close quarters maneuvering, with still quite a bit of edge going to the Yak. P-51s or 1909D-9s, will have a really hard time shaking it off if they don't have enough room to dive and extend.
As a LW plane fan, the Yak-9U is a bane to LW planes - I certainly wouldn't want to meet one on equal terms.