We LOVE the Oregon Coast!!!!
That said...the worst place to STAY on the coast would be Seaside as it's filled w/the old tickytacky type hotels (though most ARE on the beach).
Seaside does have a fun touristy trap feel about it and has the arcade, the shopping, the minigolf, the movie theater and the outlet "mall"...so nice to visit.
We really, really love CANNON BEACH...go see Haystack Rock when the tide is out and you can explore all around. Plus there are locals there w/info about the ecosystem, and some hands on exploratory stuff (you can't touch the ones in the tidepools). Plus Cannon Beach has nice eateries and a much prettier beach than Seaside.
Last time we were down, we rented a house in a little town just south of Cannon Beach...we got a beautiful house w/a hot tub, kitchen, laundry facilities and a block from the beach for far less than we ever paid for hotel rooms in Cannon Beach.