I am running an older $250 Lenovo 15 inch laptop with Windows 8 we bought at best buy a few years ago. It powers three external monitors for my work when I need to be productive. 1 through the HDMI port, 1 through a VGA connection, and one through an external video card that is VGA to USB Yes that's a grand total of 4 screens. I need more ram as I am currently maxing out the 4 GB pretty quickly. I don't render video or create music so my relatively low power Laptop does pretty well for me. I am an analyst so I need space for my spreadsheets, databases, and word documents.... So I use every square inch of my screen space.
For on the road a 15 inch laptop can get you by, a cheap 19 inch widescreen monitor is light and easy to store and a snap to set up on the road if you need the screen space. Of course bring at least a wireless mouse... Makes things easier. We also have a 13 inch MacBook Pro in the house that my wife primarily uses for her business. I really like the MacBook too, nothing wrong with either system.
My 13 year old has a ChromeBook.... Believe it or not... That is a super platform. There is a small learning curve for offline use... It can run an external monitor, but for the money and for the right person a ChromeBook could be the answer... It's so much more than just email and Facebook.
I would not and have not used a tower in over a decade, I just don't need that kind of system.
Thanks!
Jeremiah