I have two teachers that I hesitate to choose:

First choice : I have good relationship with this professor, he knows my personality very well. BUT, I just attended his course of Electronics and Circuits, which has no benefit to me. (I am interested in theoretical condensed matter physics) The Professor has good image of me but what he can write on the letter might be limited and has less connection with my research and related subjects.

Second choice : I also have good relationship with this professor, and I attend his courses of Group Theory, Complex Variables, Differential Equations. This professor specialized in string theory, which also has less connection with my interest and research. The only advantage is that since I am interested in theoretical physics, math is an important technique. This might be a little help, I guess......

The first knows me very well but has less assistance to support my research.
The second has a little relation with my interest, but does not know me better than the first
SO.....which one should I choose ????????????

THX