Brilliance is the same design as Radiance.
I think it is pretty clear which ship design people prefer (Radiance-class). Especially with some of the recent upgrades on Radiance, these are very fine, comfortable ships, small but with a nice variety of interior spaces.
I would like to try Radiance (have never been on this class). It is similar to the Spirit-class for Carnival, small but new.
Personally, if I could only take one more cruise ever, I would pick Allure (I like big ships with lots of variety), however. But after that I would want to try Radiance.