Personally, I preferred this one to The Other Boleyn Girl, which I thought was a somewhat flabby version of events with something of a problem in that Mary Boleyn is meant to be kind of an innocent and romantic who falls for Henry (on and off) but is playing a lot of court games and intrigues at the same time. So, she's "sweet" and idealistic but a manipulative social climber.... That doesn't really add up. The Constant Princess has a few plot/character problems, but not as glaring.
The two stories are inherently very different, as are the women. Catherine married a much younger, star struck Henry vs. he was holder, getting a bit bitter, and beginning to contemplate his own mortality without an heir when he started chasing Anne. I've read a lot of novels about them both, and the Anne Boelyn era makes for the most exciting fiction, while the Catherine of Aragon era makes for the more deeply romantic, I think.
:-)