Just my opinion here… But, installing onto a KVM type VPS is probably the best way to keep a long term installation.
This allows you to increase server resources (CPU, RAM, SSD) without affecting the running server. When you have been running a ERPNext server for a long time you might actually wind up growing the business that it supports and therefore need to be able to expand the system resources to meet the increased demand.
Docker images tend to try to keep everything in the container (including the database) and at some point it will become to large to handle within the container.
There are several ways to setup a container that would allow for the database to be in a separate server, but if you are going to go that far then why not just be simple about it and install from scratch on a good VPS.
This way, if you discover a problem in the installation later you can fix it yourself. In a docker image that is not really an option.
If you only want it long enough to learn to use it, then the docker image is going to be just fine. Bitnami has one that you can just run with and there are a few other similar options available in the official images.
If you want to really make use of it in a production environment, then lease yourself an inexpensive VPS server and run through the Easy Install. You will learn a great deal about how the system works and how to maintain it for long term usage.
O think I paid about $6 per month for a KVM type VPS server with 2 CPU, 4gb RAM, and 35GB SSD from company called DesiVPS. The server is in Los Angeles and it performs well for the cheap price. It is a great way to get started learning.
I have other faster and better provisioned production servers with other VPS vendors, but you may not need a great deal of power at first and you can always setup another one on a different server later and transfer the data and support files using the “scp” command.