I just downloaded and started playing both, so I am not too far in either but I am having a hard time deciding between the two. Fiesta is kind of cool but it just feels so much like every other mmorpg (so does solstice I guess but there is something there that draws me in a little more). I like the graphics in solstice because in a weird way they kind of remind me of Ragnarok.
Really what I usually look for in an MMORPG is a wide range of class customization or just a lot of classes in general.
Pretty balanced classes.
PvP isn't that big in importance, but good late game PvP would be pretty nice.
Decent armor and weapon customization (not as in making weapons necessarily but a lot of different looking weapons and armor to change one's character's appearance.
A variety of quests, so I don't want nothing but collection quests (probably not gonna happen between these two games but just thought I would mention it in case anyone has any suggestions for any other MMORPGs that fit my tastes).
Pretty bug free, Solstice has quite a few that I noticed within just 20 minutes of playing but it's new I guess.