I know of at least three of us on this board that use the Weekend Brewer regularly. I personally have no complaints about their ingredient quality. The service that you get from Bob and Jeanne is top notch, whether you are brewing beer or wine.
Do you ask because you have had issues, or because you'll be in town and want a reputable store?
I live right around the corner from the store, so I get all my ingredients through them. I know that they bag their hops in ziploc baggies--if you are traveling far you could always ask them to double-bag it.
I've never ordered from Northern so I have nothing to compare it to, just no complaints to date.
I've never gotten ingredients anywhere else, so I can't compare. It looks like they go through their basic stock (bulk extract, grains, hops) pretty regularly so everything should be fresh. Hop pellets come in a ziplock but they've always been nicely green and aromatic.
I always shop there and I've only had 1 problem in the past year with some leaf Fuggles that had gone bad. These are vacuum sealed so I don't think that was their fault unless they left them sitting out too long before putting them in the fridge.