Having two domains that go to the same site are more than normal nowadays. I ran across this with the Pest Control Company I do work for. David Wiggins the owner wanted to promote his name and get more leads by having SEO done to his site BugEvictors.com . While this is not a problem I had David get another domain that would rank well with his business. PestControlJaxFL.com was available and tells you right away what he does and where he does it. So the same site comes up regardless of what domain you go to. However doing SEO for Pestcontroljaxfl.com is a much more successful campaign because the key words are in the domain name. This can also save you money on SEO and help your SEO last longer.
If you must only pick one Domain Name then you have to decide if your whatever you are offering is something you expect people to pass word of mouth so much that you wont worry about money anymore. If not you need to have a name people can find easy when looking on Google. Think About How Your Customers Find You On The Internet. Best Answer Do Both.
BTW .coms are always better no matter what the domain sellers tell you.