Agree with ck777 about Hillsboro Aviation (after all, ck777 lives there!). It's close to some busy air space, so you get that practice, but it's at a less hectic airport. Always had friendly tower service there (well, Almost always once I figured out the taxiways).
Fall, winter, early spring: lots of rainy days, low clouds, etc. A good part of the world to learn about icing.
Personally, I prefer the dry side of Oregon, but young 'uns looking for livelier stuff like Portland.
Here's another recent PPRuNe thread about the same topic, also recommending Hillsboro:
http://www.pprune.org/forums/showthread.php?t=295546