My home PC, which I rarely use, is a single 27". My work is 2 24". The most productive I am is on my 13" air. The size of a 27" takes a couple hours to get used to, and then ur ok. My original intention was to get a 19" and rotate it next to my 27". Dell (which i'm a fan of when it comes to monitors) sells 27" which are as high as 19" are wide, making it quite seamless.
Thats the ideal combo set up ive been thinking about. I was trying out the 24" rotated but thats wayyy too much screen for me.