Hi,
While I suspect the answers you get here will be somewhat skewed (lol), I work with both AA and GA4... (spoiler alert... GA4 sucks)
1. Ease of Use
This can mean a lot of things to a lot of people... from an implementation standpoint, if you are just working with the "bare minimum", then GA4 is technically easier... you just dump the code snippet on the page and your done....
But things are usually more complicated then that... GA4 has a lot of "auto tracking" features which don't work the best, and it's often better to create your own triggers and listeners if you want better data. Turning off these features, turning off some of the auto on PII collection, etc is a bit buried, and can take some hunting to find.
Then depending on how you are triggering the tracking, like using GTM with GA, I personally find GTM very limiting and in some cases I have to do a lot more throughout targeting to get things to work properly.
Triggers are limited, to do a truly custom trigger (like listening for a JS event), you need to create code that runs on the Page Load, to run a custom JS listener for the event, then you need to push a "custom event" into your data layer, then create a GTM trigger for the data layer event....
And Click triggers, while ok, if you have a fancy link that has a image and spans inside of it...you have to target the anchor tag AND the image AND the span, etc in order for clicks to properly trigger... if you don't, any clicks on the image or span inside of the anchor won't be detected.
When it comes to reporting on your data.... GA is horrible... you can't make certain combinations of data in the interface and have to go out to looker studio in many cases, but there are still so many limitations... I know of several companies that used GA, and did 100% of their reporting using Big Query and SQL rather than GA's tools...
In Adobe, while yes there is a little more upfront setup; I see this as a strength and not a weakness. You have complete control over what is tracked, what values are passed. Is it more work, sure... is it worth it, absolutely.... and again, you can start with a super simple Adobe setup and build on it later.
As for the Adobe tag manager (Launch, or Tags, or whatever it's called now)... I like this tool way more than GTM... when I can, I will actually tag GA from Launch where ever possible... the same cannot be said for Adobe in GTM (which is overly complicated).
Reporting in Adobe is great... yes, there are some issues you might run into when doing complex reports... but for the most part, the drag and drop, the no limit breakdowns, and the ability to create reusable segments on the fly... there's no comparison
2. Features and Capabilities
As a friend of mine has often said, Adobe Analytics is an "Analytics Tool", GA is a glorified "Reporting Tool".
Adobe is a leader in the Analytics space, and they are constantly working on improvements and talk with their clients about what they want to see.... GA is more prevalent in the market due to them having a free version... but their paid version doesn't offer much more... some more custom dimensions and metrics... but it's essentially the same tool... and honestly, I can make a fancy complex report in Adobe in 30 mins... or spend a day making a less fancy and complex report in GA... there's no comparison....
3. Integration with other tools or platforms
I'm not sure what type of integrations you are interested in... but I find Adobe is far more flexible than GA... at least due to more triggering options, or custom code ability.
If you are looking for "out of the box"... GA probably has more... but that doesn't mean that the way those systems are integrating is what you want... I've worked with vendors that has AA integrations.. I took one look at their solution and said "nope... we're not doing that... that's just silly", then working with them on a better custom integration...
4. Data privacy and security
In general what type of data you collect is sort of on you... Adobe has easy to access settings about IP obfuscation (if that's what you need), and many other settings.
GA on the other hand, has a buried setting to collect email addresses automatically, and you have to dig to find that setting and turn it off...
5. Scalability
Depending on your package level, Adobe can support up to 75 props (event/hit based), 250 eVars (custom expiry - hit, visit, month, year, never, etc), 3 Lists (also custom expiry), Products, and 1000 Events (on top of the standard dimensions like Page Name, Channel, etc)
GA offers 125 Dimensions (in 360) or 50 Dimensions (in standard); and 100 events (in 360) or 25 events (in standard). There is no concept of "List". At least GA4 has a proper concept of dimensions now.. values that can be applied to a page view or to actions, etc... this was the biggest improvement from UA to GA4.
Adobe offers more items and more control, and with the Reporting Attribution IQ... you can look at multiple attribution expiries for the same event...
6. Performance and reliability
Every system has a potential for going down... in the 18 years I've been working with Analytics, I've seen Adobe have 2 major issues... Given that GA is our backup, and the fact that GA4 is still relatively new, I can't say for sure what track record they have.
I will say though, that GA uses sampled data... Adobe doesn't... so from a trust perspective, I would always defer to a system that shows me actuals.
However, one thing you will notice sometimes is that each dimension in Adobe has a report limit in the month of 2 million unique values, this can mean that some small values will show as "(Low Traffic)", the data is still available (for Data Warehouse or Raw Data Exports), but for performance reasons, the lower traffic values are removed to keep the interface faster.
Adobe can be slow sometimes to pull data, but it also depends on what you are asking it to process... a large report with a lot of metrics, dimensions and segments can take a lot to process.
Hopefully this helps.