Recommended CMS

CMS I have had experience with

Why the conditional?

I won't give advice on something I haven't used. It makes little difference though, as the first two are already the most popular of their category (general sites and e-commerce).

I limit myself to open source software. It makes little difference though, as they're still the most popular. Also open source has a much quicker fix cycle which makes it more secure than commercial software and means that any inclined person can freely download and learn how to use it.

Wordpress

Wordpress currently the most popular CMS.

It is free (of charge and in freedom) and easily downloadable. You can host it yourself, but most people download it and host on their local computers to try it out or develop.
Before installing, you Must have download a web server (Apache), MySQL and PHP.
If you're on a Mac, you can download and install everything at once using MAMP (Mac, Apache, MySQL, PHP), Windows has WAMP. Instructions for LAMP (Linux)

The installation is extremely easy, and requires very little intervention from the installer. PHP scripts take care of the hard work, but you will need to have MySQLs root password set.

Wordpress was originally created for people wanting blogs (web logs) but has become a CMS for almost everything. It uses plugins, and has one for e-commerce (woo commerce).
Wordpress is also very expandable. One installation has the ability to host many sites.

If you want to create your own theme for Wordpress, I highly recommend using underscores as a starter theme. Wordpress custom themes are for programmers rather than novices. I can create a custom theme for your Wordpress instance.

Magento

Magento is aimed directly at e-commerce. It is more complex than Wordpress, mostly because of the database, and the learning curve is quite steep. Still, it's extremely powerful software and a world leader in e-commerce. Incredibly, it's still free of charge and open source. Adobe bought Magento in 2018

Squiz Matrix

Squiz Matrix might seem a weird one to throw in there, but I have a lot of experience with it. Matrix is based on PHP and PostgreSQL is the database management system. It was completely open source until 2010, and you can still download the source as a virtual machine.

Matrix has the steepest learning curve of the CMS I use regularly and is very complex, but it is the CMS of choice for a lot of the Australian state governments, local governments and universities.

I don't want to customise or download anything

That's cool, you don't have to but isn't it good to know that the option is there if you need it? All of the web hosting services I know of can install either of these for you. Obviously you will need to be on an appropriate plan, because you will need one with at least one database and with PHP as the programming language.

As a developer, I can take care of everything for you. I don't offer hosting but can select the most appropriate for you. If your site requires customisation I can do it.