It depends really. Orbx’s has a lot of landmarks that aren’t including in Asobo’s update, and they’re going to add more in an update to their package (of course they want it to be worth purchasing still).
For instance, the skyscrapers right on the approach to London City are all modeled in Orbx’s package (while most of them are poxy photogrammetry in MS’s version), and there are nice touches like Belfast anchored in the Thames.
Considering that the price isn’t high, and that it’s going to get even more content, I’m happy to have it.