I've always looked at systems differently than most people. I don't mind having a half dozen systems, but each system must match a strict criteria. I've never owned a small format film system, having started in medium format. The only small format digital I keep is a Canon 1-series set for action/event type shoots. A few of the things I look for in any system are:
1. Does it solve a workflow problem, or is it going to introduce one? For example, I loved the Contax 645, but two meter failures (both during a shoot) was enough. I also loved the Rollei 6008, but the battery always died at the most un-opportune time.
2. I don't care if another one (or more) of my systems can do the same thing - but can this do it better/faster/easier?
3. Time is money, so is the output of this system easier/faster/better to manipulate in post processing?
4. Will *I* be satisfied with the output of this system or will I wish I used something bigger? For example, I could shoot a poster on my 1Dx and once printed, clients will probably never notice the difference. But, *I* will probably hate myself for not shooting a larger sensor once I see the poster at 40x60 and knowing that I could've done them better service.
5. I don't care about service - all camera manufacturers suck at their service and are a pain to deal with. I've routinely dropped/smashed/broken gear while shooting, so that's what insurance is for. Plus, I never buy new gear, so I'm used to disassembling and servicing my own gear. If it does have to go back, that's what backup gear is for. Canon's been good at the top of the list, but I'd never own a Sony or Leica. Ever.
6. Is the gear balanced well when set up, loaded, and in use so that I can a) not fight with it all day on tripod or b) not get fatigued if handholding all day?
7. Color is one of my sticklers. I hate having to fight a camera to get dead accurate color, even after using a Colorchecker, profiling, and matching lighting with gels + color meter. For that reason, I can't stand Nikon, not to mention the ergonomics and backwards everything.
8. Maintenance requirements. I do my own service and cleaning, but most of my gear is constantly filthy and gets beat up. I don't need a system that requires being babied to keep working. Lockups and that weirdness is normal, since software nowadays is just buggy everywhere as long as it doesn't happen all the time or randomnly.
9. Optics. Good glass and choices are a must, especially lenses with movements. Can't shoot everything with a tech cam, so a more portable system's gotta have decent methods to get at least tilt and shift. Canon has good TS-E lenses and Hasselblad H with the HTS both serve this needs while still maintaining portability.
Once a system meets these "base" requirements, I'll go spend a few weeks beating up the gear. Literally, I'll do some fast/rough paced shoots, not clean a thing, and pretty much abuse the system to see if it'll survive. The first thing that gets annoying and the whole system's gone.