The MD900 Explorer is a maintenance engineer's nightmare - requires more planned maintenance per year than any other aircraft I know, maintenance manuals are ambiguous and poorly written, spare part availability is poor. However, all pilots I know are in love with it.
I also hated to work on the B737, which is praised by many pilots, but is full of outdated systems. I was working on it together with the A320, and the contrast is huge. The latter is the most user friendly aircraft I have ever seen.