Tried both, but I much prefer SEO AP. But I would recommend looking into their new SEO NEO instead if you are planning on using SEO AP.
I've gotten really good results with new and older sites from SEO AP / NEO. Running multiple Campaigns at the same time in the background of my home PC without any performance impact.
They are pretty similar in terms of UI, Speed, and Costs if you are going to use their own recommended Spinners, Content Sources, and Indexers.
With SEO NEO you can add your OPENAI API and make really good articles within the program itself that rank really good for me at the moment and barely cost anything using GPT3 (0.3$ for 100 Articles approx)
Aswell able to use Cloud Blogs (Cloud Stacking) which seem to give a really good boost to rankings as well.
Unsure if Rankerx has any of these features since I haven't used a couple of years, but I would guess so.
In terms of stability and support SEO AP / NEO are great if you have any questions or problems. Might be a bit slow over the weekends but on weekdays they are really handy if there is anything small. And they have gone out of their way to help me a few times and given me some good tricks on setting up campaigns.
Check out the Documentation on SEO NEO if you are interested, you can see every setting you can use, etc.
Not sure if still active, but there was a Coupon for 50% off on SEO NEO "OMEGANEO". Not sure if you need to use OMEGAINDEXER for it to work but it might help someone!