My current MH I bought new and it was relatively cheap, for what I was getting. NADA valued it for more than I paid for it for almost 2 years. I didn't get that good a deal, so I put very little faith in their valuations. I wasn't concerned with depreciation since I planned on keeping it for a while.
My previous MH was a voluntary repo, which was in excellent condition. It was 10 years with 32,000 miles on it and I bought it for $7,000, which was considerably less than what was owed on it. Depreciation was definitely a non issue with that MH.
No can decide for you which is better, new or used.