They all do the same thing, basically the same way, via Simconnect and bridge modules.
Unfortunately, you will find some features in some aircraft that simply cannot be automated, because the developer has used a technique relying on a variable type that just isn’t exposed in any way outside the aircraft model. There are wishlist items to improve this situation but they aren’t being worked on yet AFAIK. However, you can get 90% of the way there in most cases. Sometimes I end up having to automate things by using Spad.neXt to generate keypresses into the sim, because you can bind keys to some features that cannot be controlled any other way.
For me, Spad is the best of the automation toolkits out there. I’ve looked at AAO and it’s cool but I think Spad does more and I find it more intuitive. FSUIPC7 is a bit different than FSUIPC6 and I don’t use it for automation in MSFS apart from using the offsets via Spad.neXt.
If you’re hunting down automation ideas, the community snippets in Spad are a fantastic resource, but also Mobiflight Hubhop because you can look up the code they’re using which will tell you which variables they are interfacing to; or you can also install the Mobiflight WASM module and add those custom events to your Spad profiles and then use them in Spad as if they were regular Simconnect or HTML events.
Also, check out Les O’Reilly’s YouTube channel; he does a ton of videos showing how to use Spad with particular aircraft like the HondaJet.