Is it better to work with two computer screens simultaneously or only one screen of 30 inches?

I am web programing a lot on my in my spare time and I love to work with two windows open: one with my code and the other with the result (web page). It is making the work much more faster and
fewer flickers in the eyes of the crossings between the windows.

I can buy now a new 27’ or 30’ computer screen, or I can keep my 22’ I have, which I like, and add another computer screen next to him and work with them both.

Do you have experience working with two screens? Is that really better? Or is it better to have one huge screen with high resolution so you can open two windows simultaneously, side by side.