There are many kinds of executors. A sole executor is someone who you nominate to carry out the terms of your Last Will alone. Co-Executors refers to two individuals who you nominate to carry out the terms of your Will together. The co-executors will have to work together so you may have to take that into consideration.
An alternate sole executor is someone who carries out the terms of your Last Will if the executor(s) will not or is unable to. Note that you do not have to always name an alternate executor. If its two individuals that alternatively carry out the terms of your Last Will, they are called alternate co-executors.
A digital executor carries out the terms of your Last Will that relate to your digital assets. Note that all the above categories of executors exist also for digital executors (digital sole executor or co-executors).
Finally, there different approaches you can take regarding the involvement of a probate court. You can specify in your Last Will if you do not wish that the probate court limits or supervises the executor. Such a person is an independent executor. If you do wish that the probate court limits or supervises them, then your executor will be dependent.