I don't know if finding a job is a factor in your relocation planning, but all three areas you mentioned have fairly high unemployment rates. According to
the Oregon Employment Department, September 2009 unemployment rates for these areas were as follows:
Eugene (Lane County) - 12.2%
Roseburg (Douglas County) - 16.1%
Medford (Jackson County) - 12.5%
Additionally, all three are pretty far from Tillamook (Eugene is the closest, a 3 hour drive). If you really hate the rain, this would probably rule out Eugene and Roseburg and leave Medford, which is about 6 hours away by car. Eugene has some great elementary schools, but I don't know about Roseburg or Medford.
Have you considered Corvallis? It's a nice college town with fairly low unemployment and closer to Tillamook than any of the other cities you mentioned. Lots of rain in the winter though. If you are looking for a drier climate in Oregon, you have to go east of the Cascades, and that part of the state is rather sparsely populated. There are reasons why extremely dry areas (including SoCal, Phoenix, Las Vegas, etc.) are unsuitable for dense human habitation in the long-run.