I made the jump from Olympus to Nikon several years ago and these are the things I recommend keeping in mind:
- When making the switch, don't focus on simply the camera body that you want. You need to factor in the entire system: body, lenses, flashes, shutter release cables, etc. Look at the big picture at how the items you need will work together.
- The camera body is the most dispensible part of the entire equation. Camera bodies don't retain their value very long and are always changing and improving. A smart photographer will spend less on the body initially if that means getting the lenses and accessories they will want long-term.
- Lenses are a long term/permanent investment and retain their value. I would recommend making your first review of the brand you want based on the lenses you will want to use initially and long term. If you think you may want to eventually go with full frame, go ahead and plan on purchasing full frame compatible lenses at the focal lengths you want instead of saving a little money now and purchasing crop lenses and have to replace them later.
- Purchase smartly, purchase once. Not only do you want to take the long view on the purchase of lenses, treat the other accessories the same way. If you need a tripod, buy a good quality one initially. If you buy an ND filter, purchase the largest diameter size you can and get step down rings so you don't need to duplicate them in the future.
- When buying a camera body, get one with two control wheels and built in auto-focus motor. The extra control wheel will allow you to easily work in manual mode with one working aperture and one working shutter speed. The built in motor will allow you to purchase older lenses inexpensively on the used market that will offer fantastic performance for low cost.
My recommendation, is I would look at purchasing a used camera body from the brand that has the lenses you will want to use. Again, bodies don't hold their value long and are actually pretty easily repaired by the manufactuer as typically the shutter is the only part that needs maintenance.
Regarding the choice between Canon/Nikon, I again would not focus on the bodies. Focus on the lenses, accesories, and the functionality of their system. I chose Nikon for the following reasons:
- They had the 14-24mm that no other lens on the planet can match. I love using the wide angle and this lens has no substitute.
- Nikon's ergonomics and functionality made more sense to me. The layout of the buttons and dials along with their menu system just seemed more natural than Canon.
- The D700 just launched and had the low light performance and high dymanic range that Olympus's 4:3 sensor could never match.
By and large, Canon has more variety in lenses and had significant advantages until recently in terms of the high end telephoto market. This is largely why Canon has such a large footprint in the sports photojournalism field. Nobody wanted to change out their lenses, flashes and accesories.
Nikon's top of the line lenses are considered by many to be better than the comparable Canon; however, Nikkor's typically carry a higher price.
If I were getting ready to make the switch from an offbrand camera system to Canon/Nikon today, I would look for a used D700. With the D800 and the rumored D600 around the corner, used D700 prices have dropped considerably.
