The external cam ones are generally pretty bad - crud tends to build up on the cam and makes it very stiff, so you think you are getting the QR really tight when in fact you are not. Internal cams are much better. The Mavic ones are very good, although they don't have a cranked lever. Royce make some superb ones (basically a Campag copy, but in stainless steel) Cranked lever, highly polished, work really well. Then you look at the cost of them... but you will never need to buy new ones.