Anyone that has the misfortune of watching short-form content will tell you that one platform just isn't as good as the other. I personally have had the same experience, i've tried all the popular short-form platforms and tried to figure out what exactly makes them tick.
Sources: 100s of hours wasted on short form content and independent testing. Independent testing criteria included: multiple accounts, VPNs and metric testing.
Watch time, the most important indicator: All platforms will base off what you like on watch time to some extent and will use that metric to drive algorithmic recommendations, some do it more then others but almost none of them only depend on it. All platforms also filter out "junk views" meaning that just staying on one video and constantly replaying it will not yield stronger recommendations of a certain type or genre of video.
YouTube shorts:
YouTube shorts are mostly driven by shorts that are deemed trending, with watch time being the closest second metric that will determine what gets recommended to you. Other metrics such as likes, subscriptions, shares are less relevant. YouTube shorts recommendations like YouTube recommendations in general are very cyclical and over tuned meaning that you will see similar if not the same videos often enough that you will notice. For example: seeing a video/short about bad apple will drive the algorithm to show you more content closely related to bad apple, but not necessary relevant to what you want. Instead of getting more vocaloid recommendations, you will most likely get: the same video just again, reuploads of the same video, remixes of the same video, people reacting and talking about the video, etc... Youtube's algorithm has become very over tuned leading to poor recommendations and this is very evident with their short form content. The shorts algorithm also employs a sort of "soft reset", meaning that after a while regardless of content that you've shown and trained the algorithm to show you YouTube will start showing you what it thinks you should be shown, which in most cases is trending shorts and very popular youtubers. Meaning that you could have trained the algorithm to only show you classical music and after a while, it will just start showing you mr. beast and other trending slop in an attempt to broaden the scope of the content you are being recommended. All platforms do this sort of reset but from my personal experience and testing the one from YouTube is the least efficient in bringing you content that actually interests you if your interests aren't the most normiest of trendy interests and videos.
YouTube after a while tends to drive away a large portion of it's short form audience simply because of how they've implemented their cyclical algorithm and soft reset. 6/10, not very addictive, easiest to quit.
Facebook/Instagram reels:
Reels are interesting because one of their main metrics for driving content is pushing content already deemed popular in the region you are currently residing in and popular with your friends. Reels are also interesting because they are notoriously lax in their TOS enforcement. This combo has earned them a very notorious reputation among those who view short form content, some of you might already know what I'm talking about. This increases their propensity to show you edgy, shocking and NSFW content drastically, as there is a culture of edgy humor mostly driven by teens. This means that if you have edgy friends and/or are residing in a region where such "humor" is popular you are very likely to see NSFW/NSFL content completely unprompted. And as most people cannot look away at first this trains the algorithm, using watch time, to show you more of that stuff. Which leads to a cycle of edgyness and gore, which to most sane individuals tends to be off-putting. This has earned reels the nickname of "liveleak lite" by the amount of unprompted car crash videos and mangled gore you are likely to see if you reside in certain regions or have very edgy friends. Now this isn't too big of a problem, as with telling Instagram that you are "not interested" in such content you can eventually train the algorithm to stop showing you that stuff. But it's not that simple, remember the soft reset that i've talked about about? Well Reels implements it as well, but unlike shorts it does it based on content popular in your region or with your friends... Meaning that you can just start seeing gore again, completely unprompted. Some have had success training the edgy out of the algorithm, with calculated uses of watch time and liking but many have failed and simply do not use reels.
An addendum: While reels are mostly similar between Facebook and Instagram, an interesting curiosity is that using reels on Facebook makes it far less likely to get the NSFW/NSFL content even if you do get it on Instagram. Why this happens I'm not sure, but at least from my testing it has been consistent.
6/10 if you're normal, 9/10 if you're an edgy re*d that laughs at gore.
TikTok:
TikTok, the undisputed king of rotting your brain and the only one that has implemented the "soft reset" protocol correctly. TikTok is the rare exception to the currently available short form in the case that it's a platform that you can truly train to show you what you want. The metrics are mostly the same: watch time, likes, follows... But what makes tiktok different is that these metrics are weighed differently in a way that your feedback actually has an impact to what is being shown. Meaning that whatever you originally get when you sign up, as tiktok uses your location, sim data and geo info to determine your region and show you content based on it, you can successfully train out of such content if you do not like it with strategic manipulation of watch time and use of likes, follows and reposts. TikTok is also different in the way it implements the soft reset, using metrics from your account, mostly your likes and follows, to break you out of the current algorithmic cycle and show you more broad content that you might like. Now TikTok is far from perfect as it tends to overweigh your metrics leading to an onslaught of similar content lead just by a singular like. YouTube for example only does this with their long form videos. This can lead to a cycle of "doom scrolling", as liking one depressive meme for example will only have you getting depressive content for the next 20-30 minutes if other metrics are not adequate. Continuing to view and like such content will also change the "soft reset", potentially leading to an even deeper "rabbit-hole" of unwanted content.
9/10 addictive.
There's not much of a conclusion to write except confirming why TikTok remains the first choice for those that want to watch short form content. It's just better.