This is posed as one question, but for me the camera I use most isn't really my favorite, so for me it's two questions.
My favorite camera is usually the one I bought most recently, but lately it has been my Leica M3. What a surprise on this forum, eh? However, I've got to admit that my guilty pleasures have often been with little 110 cameras, and a Minolta 110 Zoom SLR that I got recently falls into this category, as does my first camera, the Pentax Auto 110.
The camera I use most remains my iPhone. What can I say? It's in my pocket all the time, and it's got the second highest resolution of my digital cameras.
Scott