I am going to register a domain with a keyword but the original keywords was registered. I am thinking about other options, please advise me which one would be best in ranking order:
Any of that will be good enough. Think also about how your domain reflects your brand and what you are trying to accomplish. The key phrase in your domain is not as crucial as using your key phrase in:
your page titles
in your body content
inter-linking pages within your site
using your key phrase in hyperlinks from other sites pointing to your site