been to both, live near NW Trek... NWT is more expensive (by a few bucks), but they have some cool animals, i was actually thinking of going again to mess with that camera i got... Olympic is a pretty cool place as well, unlike NWT, they have Lions and Tigers... you can bring bread too to feed the animals as stated, but as of a little while ago, only Wheat bread is allowed, they will take any other bread you have with you before entering...

it all depends on how much you want to spend... NWT is more expensive, but its not cheap to drive to Sequim either.. both are really cool places, and have cool exhibits..