[I] think that one of the biggest mistakes when buying a camera, is to be shortsighted and think that you are buying the camera alone. You don't buy cameras, you buy camera systems.
So what is better? The OMD? or the X-pro? Or is it the Nex7? While a direct comparison is useful, if you buy any of those camera, you are essentially buying the camera system, not the camera itself. I now have a NEX7, I locked myself into NEX lenses only. I didn't buy the NEX7, I bought a camera compatible with the Sony NEX system.
When selling my previous gear for the NEX7, I sold the camera, but also the system. I sold my lenses, my adapters, and now my flashes and my triggers (that are incompatible with NEX7's hotshoe). Jumping from system to system is a hassle, and that is why I think buying a camera should be a matter of tremendous deliberation, because you will loose lots of money selling a system to buy another (except if it has cheaper components). Here's what I believe is important when looking to buy a camera system (beyond the camera itself)
One of the most crucial aspects of a camera system has to be the lenses. I think only your budget can determine the best lens lineup. If you have $1000 and dunk $500 in the body, but the cheapest lens is $800, it's bad math. I personally look at the lens lineup to have both cheap and premium glass. Leica is all premium glass, Olympus has some cheap ($ wise, not quality wise) and premium glass, etc. The selection of lenses is also crucial. If I am a low light photographer and the system's fastest lens is f/3.5 it's a bad buy. It all depends on you and your shooting style. I wouldn't care less for a zoom, but if you are a zoom shooter and the system doesn't have one, it is again a bad buy.
Legacy lens features
Most modern cameras support legacy lenses, the question is how is the experience with them. No Focus peaking is a deal breaker for me, but others swear by the zoom feature. Legacy lenses are important because they can be cheaper than available glass and some are legendary. I enjoy my Voigtlander on my NEX7 because of the focus peaking feature, if it wasn't there, I would not enjoy it at all. But now there are other features that are important for legacy lenses: AF adapters. The NEX system so far is the only one who has such adapters, like the CANON AF adapter, Speed booster, Contax G adapter. So it's ok if the official lens lineup is lacking, as long as you can have a good workflow with legacy lenses.
ExpandabilityA system camera must be able to expand to your needs, typically through accessories. If you have an OVF less camera, is there and option to get one? How are you going to get your camera to wirelessly trigger your flashes? Is there LCD hoods for it? Is there a pocket flash? A flashgun? My camera has no hotshoe, what do I do? Etc.
If you are switching from a system to another, make sure it is compatible with what you already have, or if you are willing to part with some stuff for other stuff. A simple example, here's what I had as a flash kit:- 2x flashes (regular hotshoe)
– bunch of pc sync cables
– trigger and 2x receivers (regular hotshoe)
– Bunch of accessories like Hotshoe to PC sync, etc
All are these are useless to me now: My flashes can't mount, my hotshoe accessories can't mount, my camera does not have a PC sync. Adapters from Minolta hotshoe to regular hotshoe is a no no: When i mount my flashes on it, I feel the whole hotshoe part is going to break. I had to part with all of these things above and invest in system appropriate mounts and triggers, all because my system is more proprietary (NEX6 has a regular hotshoe it seems).
All of this to say: Think twice before buying a camera, you are actually buying a system. And not that system's present, the system's past (Ex: With the Sony LA-EA2 adapter I have access to Minolta AF lenses of the past) and the system's future (The new lenses, accessories and whatever crazy thing in store).