I entered the semi-professional aspect of photography a few years ago and began swimming in the sea of options that is modern dSLR photography. I had been using a very nice Canon superzoom camera (SX20IS) and had invested in Canon peripherals like speedlites, so I felt like I wanted to stay with Canon. My first purchase was a Canon Rebel T1i. I came to believe (and still believe to a certain extent) that the quality of the glass is more important than the camera body. I have seen amazing pictures taken with the most humble of dSLR cameras. But I began to learn that there were other factors than image quality. Handling, for one thing. That led me to my second dSLR purchase...the Canon EOS 60D.
I love my 60D. It is so intuitive and easy to control. The flexibility for video is unmatched by any other dSLR that I have used. The articulating screen is surprisingly useful. And I discovered that when it comes to challenging lighting conditions, not all cameras are created equal. I quickly began to see a big difference in my photos taken at higher ISOs when compared with T1i.
I eventually determined that I wanted the flexibility that having both a full frame and a crop body (APS-C) would offer. I started saving (and shopping) for a 5D MK2. I purchased one a few months back and have been familiarizing myself with it since. At this point I have used an entry level sDSLR, a semi-pro body dSLR, and a pro dSLR. Here are my observations:
1) The 5D MK2 is a fantastic camera, but when it comes to handling, my 60D is my favorite. Live View is better implemented. Video function is more intuitive. The articulating screen is a big asset. The on/off switch is more logical. Those extra two years along the engineering cycle show.
2) Nothing beats a full frame when it comes to low light performance. The 5D MK2 laughs at ISOs into 5000+, and I understand the MK3 is even better.
3) Full frame produces slightly more saturated color. That big sensor stores a huge amount of information. I once produced an HDR .jpeg from it that was over 28MB - a jpeg! That is a lot of color info!
4) A crop sensor is both a blessing and a curse. The extra reach on the telephoto end without a loss of image quality or aperture size can make a huge difference. On the wide end, however, common lens like a 70-200mm often aren't wide enough. There are few lens designs that imitate the 70-200mm focal length for an APS-C body.
5) Some lens come alive on a full frame sensor. The full frame sensor is far more demanding...yet some lens just seem to love it. Other lenses are "shown up" by their sub-par resolving power on a full frame, but good glass really shines on a full frame.
I consider myself very blessed to be able to enjoy the best of both worlds.