I was just up in Portland a couple of days ago, deliberately hitting a few hills, but it is a good reminder that there are lots of hilly places in the city.
So, is your commute flat or hilly? I would think that would be one of the big determinations if you need some kind of motor assist.
Are your loads compact or bulky?
For me, a small backpack is handy for small things. If I expect to carry mid sized loads (up to 100 pounds or so), I just snag an ex-kid's trailer. Although a small cargo specific trailer would be nice.
For larger loads, I have a home-made cargo bike. I've carried up to 100 pounds on the bike, but I typically just use it to pull my heavy hauling trailer which can haul as much as I can pull (up to about 500 lbs or so). I don't go real fast pulling 500 lbs, but I have a couple of moderate hills that I'll pull it over. I NEED LOWER GEARING!!!
I very much dislike driving and parking in downtown Portland. So, a bike can be very handy there. And in the inner city, the bike is just about as quick as a car. But, the bike is somewhat limited with distance. 20 miles each way can get quite far in Portland, but any further, and a car is definitely nice.