Of the Exaktas, I've found the VX500 to be the best of the lot, in user terms. Ihagee quality started going down the tubes when the VXIIB came out, and got worse with the VX1000. When they were rolled into VEB Pentacon, the quality improved a bit and the VX500 and the last of the VX1000 cameras are actually pretty decent shooters. But the VX500 does away with the intricate self-timer/slow speed mech, they're lighter and more robust because of it. The VXIIA and earlier cameras exhibit a nicer fit and finish than the later cameras, but the shutter curtains are made from a material that self destructs with age - and in any event all of them should be cleaned and lubed before use - it's just the cost of replacing the curtains on top of that can make the older Exaktas quite pricey. The VX500 is simple enough that it an be opened up dusted out, and oiled, at home by anybody with the right tools and mechanical finesse. I've never even had to mess with the shutter tension on any VX500 I've opened, just clean and lube and it's good as new.
The early Prakticas I generally stay away from. They're loud, crude, and huge. Then the Novas come and are supremely unreliable. The revised Novas (that is with the modern shutter dial instead of the old lift-and-set type) are serviceable... but the shutter times can be all over the place even if the camera sounds like it's working correctly. The later L series cameras are a better bet.
My favorite? The Exas. It's rare to find one that doesn't work perfectly. I've encountered just a few problems through the dozen or so I've had. The original series cameras have a light seal behind the mirror made from the same self-destructing material as the Exakta shutter curtains. This seal cannot be replaced. It's rare that it happens, but sometimes you get a light leak here. It can be painted over with fabric paint for a simple fix though. Shutter capping is another issue, caused by dried out lubricants, this is a simple fix, open the camera up (no special tools are needed, just flathead screwdrivers) clean out the old grease and oil, and relube - the Exa will be good for another 60 years.