Both BLI and MTH make good streamlined steam locomotives, and they both make top-drawer coaches. I can't speak from experience on behalf of MTH, but I can speak with considerable experience on behalf of BLI. They have quality problems no better or worse than any other manufacturer of HO scale rail items, and their repairs are at least as good as any other a body could claim is the best. I doubt you'll have more than a modest expenditure headache for shipping items insured back to their repair facility, but I can assure you that they satisfy 99% of their customers by the time they return a defective unit. I know of a couple of complainants who had to return an engine a couple of times, or more, before they got satisfaction, but they are in the reported miniscule minority.
If you ware willing to move further afield from strictly streamlined steamers, Bachmann, Rivarossi/Hornby, and Athearn make very good steamers and the warranties for Bachmann and Athearn are rather good. I have never returned a Rivarossi engine, but I had no trouble getting free small parts for my H-8 Allegheny 2-6-6-6. They are in the NE of the USA, and I asked to get a mechanical lubricator arm, a teensy little sliver of metal. They sent two free of charge.
In BLI's case, I have a history of two at-fault repairs for which they charged me nothing, and one was a QSI decoder. Not so shabby, eh? I am still out-of-country, and so are you. I don't see why which side of the Atlantic/Pacific you are on should have an impact on their desire to come to the good. You'll be well served, but short a few coins to get it back to them at most.
Sorry, I have no experience at all with Con-Cor.