Largest triangle to fit in a circle will be isosceles triangle? Largest triangle to fit in a circle will be isosceles triangle?
Or some other type?

Yes, what you say is true, but you can say more than that.
Given a particular chord of a circle, you can maximize the area of the triangle by having the third vertex as far away as possible (area is half base times perpendicular height), which means that it will be on the perpendicular bisector of the chord where it crosses the circle, the other side of the circle's centre.  So with this chord as an edge, the area will be maximised if the other two edges are equal, i.e. if the triangle is isosceles.
But the same thing is true of the other two edges, and that implies ... (I will leave you to work this out) 
