By turn based, do you mean such as for battles like in Final Fantasy I-III, Chrono Trigger, etc?
The RPG Maker series does that.
XP seems to have the most resources, along with VX, but there's a whole debate over which is better.
Now there's RPG Maker VX Ace or whatever, which I heard is great, so...
If you mean turn based like... Advance Wars or Fire Emblem, then I don't know any great engine for it.
There was a planned FE-like engine, but it was stopped after some incident about it being leaked.
I've never heard of Sphere, but if it suits your purposes and you decide to use it, then good for you.
What does it cover, anyway?