Quote Originally Posted by Santiago Rosa View Post
Just got SSR Eidolon Thunderbird, so if a SR Princess is better should I exchange?
It depends on the SR Princess. Some are stronger and are unique enough that makes them more valuable than a SSR Eidolon. One of the strongest SR Princess available from the pre-reg is Brynhildr. Bryndhildr is almost especially strong in the early game because she is the only healer available in the fire element.

On the other hand, Thunderbird's summon effects are kind of situational, removing detrimental effects can be necessary to some bosses and absolutely useless to other bosses. Situationals are rated very low on my list. So unless you plan on having Light or Thunder as your main element, I would probably replace Thunderbird with something with more versatility.