I'm a multi-family broker in Portland, so this will sound a bit biased... I say focus on multi-family. There is nothing indicating a slow down of people moving to Portland. And since nothing is being built in their price range to buy, they are willing to pay a lot more for their rent. The only issue I see is with how much money you have to invest.
$100k won't get you a 4plex in (or tri-plex for that matter, in fact we just sold a duplex for $690k) unless you are buying it owner occupied. 5 or more units will put you in to a commercial loan situation (which isn't bad, just different) and you'll be in the $600k range minimum. You won't be able to hit your DCR if you only had $100 down, which you'd need at least $150k for the down payment. This numbers are for the areas that I think have the greatest opportunity to appreciate. You can go to other areas just outside the core of PDX and get more property for your buck, but you will not see the same type of appreciation.
Also, remember that the value of multi-family is primarily based on the income that it produces versus the expenses to get there. So even if the "market" appreciation remains flat, but you can cut expenses (billing back for utilities instead of paying them your self) and move rents up slightly, you can add a lot of value to your property. Forced appreciation.
With SFR, you will always have more buyers if you are planning to sell it in a shorter time farme, but the downside is that all of your income is tied to one tenant. If they leave you high and dry, or worse just decide to stop paying and drag you through the courts, it can be months of you covering all of the costs. This just happened to a friend of mine. With a multi-family, you will have those other tenants covering their portion so the risk is spread out.