The 6x4.5 and 6x9 come closest to the aspect ratio of the 35mm that you're used to. You may find composing the square 6x6 format challenging. I've been playing with it for about 3 years and am only now getting results I like. That being said, it's been a really enjoyable experience. I have been using a 1948 Zeiss and a Mamiya C33. They are both 6x6, but are about as different as 2 cameras can be. No other tlr can match the flexibility of the Mamiya C series and they are very high quality in design and manufacturing. They are pretty heavy to carry around, but can be had at bargain prices. The Zeiss design goes back to the early 30's and has a charm of it's own. Be careful - once you experience MF you may never want to go back to 35mm.