These 3 licenses are best for Open Source

Choosing an open source license is confusing.  There's so many!  But I've narrowed it down to the 3 best ones for me nowadays.

I'm not a lawyer, so take this as entertainment.  :)

1. Apache License 2.0 --- Apache-2.0 @ SPDX, ChooseALicense
2. Mozilla Public License 2.0 --- MPL-2.0 @ SPDX, ChooseALicense
3. GNU General Public License 3.0 or later --- GPL @ SPDX, ChooseALicense

Which you use depends on what kind of sharing you want to do.

Use Apache 2.0 license if:

1. you want anyone to be able to use your code however they want, 
2. including building bigger projects based on your code with the bigger work licensed however they want (including possibly "all rights reserved" proprietary licensing), 
3. without expecting them to share anything back in return,
4. without expecting them to acknowledge they used your code,
5. and without expecting them to share your code that they used.

Use MPL 2.0 if:

1. you want anyone to be able to use your code however they want,
2. including building bigger projects based on your code with the bigger work licensed however they want (including possibly "all rights reserved" proprietary licensing),
3. but you expect that any changes they make to your files are shared back in return,
4. you expect that they will acknowledge they used your code,
5. and you expect they'll make available your code that they used.

Another great thing about MPL 2.0 and Apache 2.0 is that they are compatible with each other!

Use GPL if:

1. you want anyone to be able to use your code,
2. including building bigger projects based on your code but with the bigger work also GPL licensed,
3. and any changes they make to your code, as well as any code added to your code even if in other files or modules, are all shared back in return,
4. you expect that they'll acknowledge they used your code,
5. and you expect they'll make available your code they used, and also any code they add, even if they added them in other files or modules.

Notice the big distinguishing point is in how much you want users of your code to share back changes or additions.  From zero sharing required (Apache 2), to sharing changes or additions to your files (MPL 2), to sharing all changes or additions whether they be in your files or in other files linked (dynamically or statically) to your files (GPL).

If you want help navigating to which license to use, this License Selector I found the best (except it's missing EPL-2.0).  While the Choose a License site from GitHub has the slickest UI, they make some questionable suggestions from my point of view, like highly suggesting the MIT (a.k.a Expat*) License instead of the Apache license.

One reasonable advice from ChooseALicense though is to choose the license common in the community you want to share in, but that's really only true if there is an equivalent license to what you'd otherwise want to use.

For example, if you want to use the MPL-2.0, but you're wanting to share in the Clojure community, then you're probably better off using the EPL-2.0 (Eclipse Public License) instead, despite the EPL 2 being very likely not as "good" as the MPL 2 by some metrics.  But EPL is only even an option as it's basically equivalent to the MPL as far as I could tell.

If for some reason you really wanted to GPL license your Clojure code, then EPL isn't going to cut it anyway because they're not at all equivalent.

* this is different from the MIT / X Consortium License.