If you have any inclination to partake of the evening festivities (i.e., the alcoholz) then I recommend staying closer to the venue. It's harder to stumble home if you are far away. Even if you don't intend to, it's generally easier if you're closer since keynotes start around 8AM and BOFs go to 11PM or later. If you want to maximize your networking and social/event time, then it's really grueling if you also have to add a commute to that.

OTOH, if you stay west of the river and near downtown, Portland is a nice city. Fun to walk around and see things. So there are really good arguments to be made both ways...

Also, also, it's nice to stay near other people who are going. I will certainly find whatever hotel is closest to the venue and make my reservations there. I hate commuting to conferences. I should probably take care of that...