You can't really compare them apple to apple with such brief specs. Take a look of this Rotel's THD+N vs power output graph:
Rotel RB-1090 power amplifier Measurements | Stereophile.com
You will find that typically for a class A/B amplifer the distortions would tend to be higher at very low output, levelling off as output rises to approach say 1W and then it would rise sharply at near the so called "rated" output and beyond. In this case Rotel is probably providing those lower THD figures at 1W output while Crown's at rated output, hence higher.
That being said, the Rotel likely still will have better specs but that most likely would not translate into audible improvement to all but those with highly critical hearing abilities. You are not limited to the high cost Rotel either if you are open to the used market, but in that case go with something that has a transferable warranty.