Should conda, or conda-forge be used for Python environments?

The short answer is that, in my experience generally, it doesn't matter which you use.

The long answer:

So conda-forge is an additional channel from which packages may be installed. In this sense, it is not any more special than the default channel, or any of the other hundreds (thousands?) of channels that people have posted packages to. You can add your own channel if you sign up at https://anaconda.org and upload your own Conda packages.

Here we need to make the distinction, which I think you're not clear about from your phrasing in the question, between conda, the cross-platform package manager, and conda-forge, the package channel. Anaconda Inc. (formerly Continuum IO), the main developers of the conda software, also maintain a separate channel of packages, which is the default when you type conda install packagename without changing any options.

There are three ways to change the options for channels. The first two are done every time you install a package and the last one is persistent. The first one is to specify a channel every time you install a package:

conda install -c some-channel packagename

Of course, the package has to exist on that channel. This way will install packagename and all its dependencies from some-channel. Alternately, you can specify:

conda install some-channel::packagename

The package still has to exist on some-channel, but now, only packagename will be pulled from some-channel. Any other packages that are needed to satisfy dependencies will be searched for from your default list of channels.

To see your channel configuration, you can write:

conda config --show channels

You can control the order that channels are searched with conda config. You can write:

conda config --add channels some-channel

to add the channel some-channel to the top of the channels configuration list. This gives some-channel the highest priority. Priority determines (in part) which channel is selected when more than one channel has a particular package. To add the channel to the end of the list and give it the lowest priority, type

conda config --append channels some-channel

If you would like to remove the channel that you added, you can do so by writing

conda config --remove channels some-channel

See

conda config -h

for more options.

With all of that said, there are four main reasons to use the conda-forge channel instead of the defaults channel maintained by Anaconda:

1. Packages on conda-forge may be more up-to-date than those on the defaults channel
2. There are packages on the conda-forge channel that aren't available from defaults
3. You would prefer to use a dependency such as openblas (from conda-forge) instead of mkl (from defaults).
4. If you are installing a package that requires a compiled library (e.g., a C extension or a wrapper around a C library), it may reduce the chance of incompatibilities if you install all of the packages in an environment from a single channel due to binary compatibility of the base C library (but this advice may be out of date/change in the future). For reference, see the Conda Forge post on mixing channels.

Anaconda has changed their Terms of Service so that "heavy commercial users" would have to pay, which doesn't include conda-forge channel.

The main channel is maintained by Anaconda, while conda-forge is maintained by the maintainers of the packages themselves. Each have their pros and cons. Packages on the main channel are usually compatible with one another, meaning you can install almost as many as you want, and you won't have dependency conflicts. On the other hand, packages on the conda-forge channel receive the updates much faster than the main channel since the maintainers themselves push the updates to the channel. From time to time, there are also patches done by Anaconda on packages available on the main channel which are not supported and done by the maintainers of the package, which can be good or bad, but definitely out of hands of the maintainers and not supported by them.

You probably would want to stick to conda-forge if you don't want to pay for the usage and you would be okay with the versions available on pypi. As stated in the docs:

conda config --add channels conda-forge
conda config --set channel_priority strict
conda install <package-name>

You could also use miniforge which has conda-forge as the default channel, and supports ppc64le and aarch64 platforms as well as the other usual ones.

If you have conda installed and would like to remove the default channels, you can use

conda config --show channels

to see your channels, and can use

conda config --remove channels channel-name

to remove a channel.