The topic of respirators has been brought up in another thread, and I ought to shop for one too. What features (other than the proper filter cartrige) makes for a really nice respirator? Are there certain ones or styles that are absolute junk or irritating to wear? Is there a "Cadillac" model or type of respirator that is especially comfortable to wear? Anyone use one on a regular basis that they especially like? I leafed through a safety supply catalog, and there must be 20 models of basic respirators, not counting the ones with external air supplys (which I don't need).