First of, I would never own an iPad or any other 10” tablet. I strongly prefer the 7” form factor as i can hold it in one hand. Anything that requires more than that amount of screen is better done on my laptop.
For most things, I go in Portrait mode on my tablet because i like a narrow keyboard, and because it’s easier to hold that way. However, my phone often winds up in Landscape when i am typing. As for reading, portrait fits most things I have better.
Note also that i never have mine on a table. I find that to defeat the purpose of a tablet, which i consider to be something for when a laptop is either overkill or just too big. Similar logic applies to my disdain for laptops over five pounds, or with a battery life under six hours. Portable electronics are portable; if you are going to use it like a desktop, then save some money and just get a desktop!