I have a paladin of Shizuru as well as an oracle who is a devout follower of Sarenrae.
I never really thought of them as particularly comperable until you pointed out the whole Sun diety thing.
I think it's how I focus on different aspects with the characters...
For my paladin of Shizuru, it's about honor and legacy - specifically how your actions to improve the world will honor your ancestors and make the world a better place for your descendents. In his case, he strives even harder given that he believes he is living penance for father who gave in to the temptations of the Worldwound and the dishonorable mother who bore him.
For my follower of Sarenrae, it is more about temperance in actions and being less the force of change, and more the fulcrum. He feels that the Dawnflower would want him to learn from her lessons that passion is an excellent thing, but that sometimes it can cause you to be led to misfortune by your enemies. Temper always your penchant for violence with vigilance in recognizing your motives, but never quell your desire to give aid and comfort to your allies or the victims of evil.
Were the two to ever meet, I think they would both be interested in seeing how the other seeks to better the world they live in and those they call allies & friends.
Tsukiyo is an interesting diety as well. I'm with you on the uninspiring longspear (wish they had gone with something a bit more flavorful, like a Naginata, but eh), but the Lawful Good diety with the Darkness, Madness & Repose domains can make for some evocative character concepts. I was pondering an aasimar follower of Tsukiyo with a sort of "guardian in the night" or "slightly crazed undead hunter" touched by the higher planes concept, but I doubt I'll get to play it before the cut next month.