Distance from terminal at PDX to heart of downtown is roughly 12 miles - http://goo.gl/maps/03e09 Are you renting a car, taking a taxi or using MAX? Cabs generally run $35-40 (estimate 15-20 minutes, but traffic can double that time), rentals are available at airport (but a couple are located off site and prices are generally a good bit higher at airport vs. downtown); MAX will cost you only $2.50/pp (estimate 45 minutes to get downtown).
Most of the hotels you mention are within a short walk of MAX stops (both for getting to/from PSU and to/from Rose Garden and also from PDX, if you choose to ride it from airport). I'd opt out of Waterfront/Riverplace/Convention Center only because none are in the heart of downtown - and I'd want you to be in the midst of it all vs. on the fringe, y'know? Marriott City Center, Westin and Courtyard City Center would be my top picks. Buutttttt... take into account that virtually all of these will charge a nightly valet parking fee of $25-35, worth factoring in if you plan to rent a car and keep it overnight.
Re: PSU. It's a rapidly expanding/transforming campus on the south end of downtown. The South Park Blocks give it a pretty look and 'collegiate' feel, but many new buildings (halls & dorms) are growing the boundaries eastward. I took a few classes in their Education Department a while back (good post-grad programs) and have visited their Architecture and Urban Planning Departments (both reputable) a few times. Does your son know what he wants to study?
More good general info: …wikipedia.org/wiki/Portland_State_University
PS: Go Blazers! ;-)
Edited: 5:07 pm, October 22, 2012