When comparing PICO-8 vs Defold, the Slant community recommends Defold for most people. In the question“What are the best game engines for point & click adventure games?” Defold is ranked 24th while PICO-8 is ranked 38th. The most important reason people chose Defold is:
Defold uses Lua, which is regarded as an easy to learn language by most.
Specs
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Pros

Pro Takes away the pain of having to wire things together
Because it's an all in one product, you don't have to worry about things like how to load sprites.

Pro Very simple programing language
It's lua with a few modifications.

Pro Encourages building simple games
As a beginner it's all to tempting to try to make the games you like to play, like Zelda or Call of Duty when we should probably be making pong.
Pro Restrictions of tokens count "forces" to write code effectively
When you reach 8192 tokens, you're screwed. However, this limit can teach you to take a look at entire code and think how you could optimize it.
Pro Possible writing code in external editor
Since launch of 0.1.12c version of software, you can now write and include external script using the same directive just like in C / C++.

Pro Perhaps one of the easiest sound editors around

Pro Share the game in a .png file with other Pico-8 users

Pro You can read the code of any game you play

Pro Lots of examples
Almost every game made for the Pico-8 is open source (if you can download the .png, you can see the source).
Also there's the fancy Pico-8 "fanzine" that has lots of code examples as well as other great tutorials in a beautiful physical or PDF form.

Pro Easy to get things going very quickly
Pro Easy to learn
Defold uses Lua, which is regarded as an easy to learn language by most.
Pro Completely free of charge
Software and online dashboard are free of charge.
Pro Good combination of visual editing + code (Lua)
You can do a lot with drag and drop, but you're not limited -- the code (Lua, which is easy to learn) allows you more power than just visual editing usually gives you.
Pro Fast results
Going from idea to result is very important for the creative process.
Pro Visual editor
Pro Very performant
Being crossplatform it is important to work on low end devices.
Pro Easy and fast export for various platforms
Pro Great community
A very active and friendly community in forums.
Pro Source code available
You can download and modify the source code of the Editor and the engine for free.
Pro Collaborative
You can invite friends from the dashboard and create games together.
Pro Hot reload
It allows you to change scripts in a game while it is running live. Common use-cases is to tweak gameplay parameters or to perform debugging on a running game.
Cons

Con No collision library or other common things
Pico-8 is very minimalistic and as such doesn't come with really any abstractions whatsoever which means often you end up re-inventing the wheel.

Con Code editor leaves some things to be desired
Such as code completion and automatic indentation.

Con Costs 15$
Unlike many of the other frameworks it's not free. However this is kind of a feature because it means it's much more likely to be supported.

Con Memory restrictions could be confusing or frustrating to a beginner
