That is pretty subjective...and we generally do not buy on the internet, instead preferring to support our neighbors by purchasing locally. We have found that local businesses can match or beat internet pricing and provide service after the sale. But if you do not have a local outlet for door knobs, try this internet retailer:

http://www.signaturehardware.com/

I also recommend that you order from a local supplier as opposed to online. One of the main reasons is your local supplier will provide better service and support when you need to replace a missing part or have trouble with a product.

If you are looking for cabinet knobs you might want to consider TopKnob.
If you are looking for door lock sets you might want to consider Emtek.

I have found both to be reasonably priced and of good quality.