Your ideal domain name depends on the initial purpose of your website. Is it a personal website, or a company website? Is it advertising a service?
If you're looking for a site for your company, the most ideal domain name would be the name of your company. If this is unavailable, i.e. taken by a competitor, what is the closest domain name to your company name? Is your company's website going to get confused with another company's website due to a similar name or slightly different spelling, and will you therefore lose customers to your competitor? Has your competitor got youridealwebsitename.com but not youridealwebsitename.co.uk? In which case, would it be worth buying the latter, or would it be best to purchase a more unique domain name?
The best domain name you can possibly have is one that describes the service you're offering, or contains your company name, and one that is easy to remember and spell.
You can check which domain names are available for purchase here.