Personally I would pick only one that customers ever see. The others can remain as ways to catch typos
This. ^^^
Don't confuse your clients with intentional multiple URLs to the same site. Give them one primary URL, preferrably a *.com, because "com" is what most people are accustomed to in the US.
Then figure out the two or three most likely typos or misspellings, buy them, and redirect them to your main site. One common typo of my URL used to send clients to a French transsexual support forum. I found out about it when a couple of clients called and asked, "Is that where I was supposed to be?" I waited a year for that URL to become available, then I bought it and redirected it to my main site.
I use a "mother" *.net site as a base because I also use temporary URLs that point to pages on my site that I put up for limited special projects. My *.com address is redirected to the index page on my *.net site.
I also have a mobile site in a folder on the same site--it has its own shorter URL (because it's harder to type with one's thumbs), although my main site index page does have a prominent link to it. I'd like to automatically redirect mobile phones from my *.com to my mobile site, but I haven't found a good method to automatically detect every type of mobile phone that doesn't require constant updating.
When you get into mobile phone sites, you have to make a decision of whether to make that one a *.mobi or an m. subdomain, then redirect the other option to it. In my case, my mobile site is an m. subdomain and I have two *.mobi URLs that direct to it.
