Do I think hold different weight? No not really I'd say maybe the science professors would as they've been the standard LOR requirement for a while now while the committee letter is still relatively new as a replacement for them. As far as I know schools do like them however. If you have the ability to get two letters then I'd say go for it, or maybe work with someone in the department about getting a committee letter on top of it. It was easier for me to get the committee letter with the great support at my school and I believe the letter allows schools to see the student more than just an A in a class (unless the professor knows you well of course). The committee letters should technically tell more about you, how successful you are as a student as a whole, and why that school should accept you. The writers on my committee letter were one of my professors, the dean, and assistant dean of the department. Hope this helps and if you have anymore questions let me know or PM me.