My first two recommendations would be either the Kimpton Riverplace or The Nines. Both are located in or near downtown Portland with access to MAX lightrail or streetcar as well as beautiful catered banquet rooms.
Kimpton RiverPlace Hotel (1510 SW Harbor Way) is located on the waterfront next to Tom McCall Park and is a six-minute walk away from the streetcar. Its proximity to the river, marina and park offer beautiful panoramic views, shopping and close access to many venues including the Keller Auditorium. Depending on time of year there may be festivals in the park or on the water.
The Nines Hotel (525 SW Morrison) is in the heart of downtown across the street from Pioneer Courthouse Square and Pioneer Mall. Just steps away from the MAX lightrail and many venues such as Arlene Schnitzer Hall. It also has an amazing pan-Asian rooftop bar/restaurant called Departure — Executive Chef Gregory Gourdet was named a runner-up in Top Chef.
Other great options are Hotel Monaco (506 SW Washington), Benson Hotel (309 SW Broadway), Hotel Vintage (422 SW Broadway) and Hotel Modera (515 SW Clay) — all of which are in the heart of downtown Portland.