Frame Size

[D-50]

I am getting some photographs together to frame and display. I am putting up about 6 photos, 3 per wall, and was wondering about the sizing of the frames and prints. Initially I wanted to do everything in 11x14 but as I am looking at my photos I am finding 11x14 does not work for all of them. I wanted to have all the frames the same size for aesthetic purposes but now I am not sure if have different size prints in similarly sized frames will look odd. Should I keep the matte size the same and build the frames to fit a constant matte of say 2 inches around the print or should I alter the mattes in relation to the print to fit a constant frame of roughly 15x18 give or take? This is my first public display of work so I want to make sure everything from the print size to the matte size to the frame size is pleasing.