If you don't have a lot of assets, and are giving most or all of these to your spouse, your spouse is a good choice. Adult children may also be a good choice, because of their familiarity with the assets of the estate, and the likelihood that they may not charge fees for their service.
Friends and business associates may be a good choice, provided that they have the ability, integrity, and some knowledge of the assets and the beneficiaries. The requirements of friendship are not necessarily the qualities of a good executor. Executors may be required to run the family business, or possess investment knowledge. Depending on the complexity of your estate, these are crucial considerations.
Age may also be a factor where there are long-term trust arrangements to be put in place. For example, where there are infant children involved, it may not be wise to appoint an executor who is significantly older than yourself.