SFH split into two versus naturally built duplex

[Jeffrey Grieshop]

What my title and description state, please help. I am trying to run some comparables and get a good feel for how I should be comparing these two's values. I think a structured duplex should be of bit more value. They were built as such so the rooms should have a better aesthetic as a whole or layout, correct? Often times duplexes come with two garages and a hacked SFH may not, so I am aware of the value of an extra garage. That is of $10k value or so, agree or disagree? I think that's about where Anson Young placed the price of one in a video or discussion I saw from him(Denver area market). Heck, it might have been upward of $20k, I now forget.

Please help with the original subject though. Let's say we have identical multifamily buildings, units of 2. Literally identical in year built, sq ft, condition, location, etc. However, one is a duplex with one extra garage and the other is a hacked SFH, which value comes in higher? at what percentage?