We just purchased a used 2005 HR Endeavor with 400 isl. We LOVE it! The layout has lots of room and is so much better than the newer ones. Quality it great! Our motorhome had 15k when we bought it in June and we now have 18k. We have found minor issues each time we go out but they were all DIY items. Ours was well maintained by the previous (original) owner. If you buy used, that is important.
We have talked with the HR engineers and they are very helpful. We needed to know if there was a brake for towing (previous owner did not know). The engineers were very willing to help and they knew everything about our RV as it came off the factory floor. Loved their service and they were very helpful!
HR & Monaco (IMHO) are very equal in quality and finishes as long as the models are similar. 2005 was a peak year for many of these coaches. No sure what the quality was after 2009 with the shake-out of the rv industry.
Good luck with your shopping.
BTW...based on another post on this forum, HR will be introducing the Endeavor again. The dealers will have a preview Dec 1.