It's just a trade off, softer is weaker; harder is stronger. Buy whatever suites your purpose.
Sorry, Rhino currently does NOT have a written nationwide lifetime warranty. They tried by assessing dealers money for a warranty pot. The dealers rejected this, so back to the usual warranty by dealer only. Call Rhino corporate yourself, I did. Notice that Rhino's website is TOTALLY silent regarding a warranty. If they had a warranty like LINE-X, you would think they would want to advertise it.
http://www.rhinolinings.com/RL/main/