Regardless of the TLD in which you elect to register your domain name, assume there will be competition for the name you want. "Uniqueness" means that there can only be one owner of any given name within a top-level domain: the existence of XYZ.com may force you to consider XYZ.net or XYZ.biz if you want to use the name XYZ. (Whether you can use the name XYZ at all if someone is already using it is a trademark issue: see our primer for more on that question.)
An alternate solution is to register a variant of your company name in your chosen TLD, as in "XYZCorporation," "XYZSoftware," or "XYZonline." Again, these considerations should be discussed before beginning a naming program: what variants will you be able to get behind and promote in your on- and offline advertising and other verbal branding? Be honest. If you really want to be XYZ.com and won't be happy with any variant, then you'll have to live with the choices that imposes on the names available to you. If you will consider other TLDs and other variants of your corporate name, you broaden the parameters and increase your chances of finding a registerable domain name.