Input needed on rent pricing - upstairs units v. downstairs units with private yard

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We're closing on our first 4-plex at the end of this month (yay!).  The building is two stories, two units up, two down.  The lower units each have their own moderately-sized enclosed yards with a small, paved patio area and some grassy area as well.  We are wondering how to price the units compared to each other, so my question is what is more valuable to tenants - an upstairs unit where you don't have someone trampling overhead (and increased security), or a downstairs unit with its own yard?  Or do the differences somewhat equal each other and we should just price all the units the same?  I know this will depend on the area (its in Everett, Washington for those who know the area) and the specific tenant, but I thought I would put this out there in case anyone has noticed general trends in preferences amongst their tenants for these features or those professional property managers who may have specific data on this kind of thing.  Any input is much appreciated!  Thanks!