I like Sayaka as much as Touko x Yuu now.
Why not going for threesome, cuz seriously that's the best (and shittiest) solution.
Touko x Sayaka, i preferred that ship than the Touko X Yuu, for me, I preferred that Sayaka win the Touko's heart and stay together at last for a while... although I know that this story will end with the first couple...for me, The Touko X Yuu are a very out of balance...for a girl who did too much and another who did nothing than use the first girl like a Toy for her depression
Dunno, Touko x Yuu is actually perfect. They complement each other and both are actually very dependent on their partner. Yuu might not look like that, but remember that Yuu always lacks initiatives, and it is Touko who helps her to take the first step. Yuu is also as greedy as Touko - Yuu actually seeks to influence Touko (the theatre play arc) as much as Touko indulges on Yuu.
It is Sayaka who is unbalance to Touko. She does not try to cross the line and serves Touko without question. She can be a perfect sidekick, but as a partner, not.