Comparatively, brass is a very soft metal. For example, it is used for plumbing fixtures because it is easy to work with and easily tooled. Brass is not as hard as bronze.  Brass  is also prone to corrosion, so most plumbing fixtures are coated with another metal such as chrome to make it more durable.  You will find that a brass bell does not sound as pure as a bronze bell.  Brass bells have a "clangy" or "brassy" sound to them.

Bronze on the other hand is very hard and can last forever.  In fact, there are several grades of bronze. A type called  admiralty bronze was used for cannons and is used for propellers on boats.  

Bell Bronze is the purest type of bronze in the bronze family.  Not only is the copper content higher than traditional bronze itself (traditional bronze is 80% copper, 20% tin), there is no contamination from other metals in the alloy.  This is the reason that a bronze bell rings with perfect tone and clarity.