For me there would be no hesitation - I would buy the Toshiba. I am a dyed-in-the-wool Toshiba laptop fan. I've had three of them, and not one of them has put a foot wrong. The build quality is generally excellent, and they are good, solid all-round performers. The one you're interested in is a lovely machine.
At first glance the Dell looks great, too, and Dell does make some nice machines. This isn't one of them in my opinion however. Performance-wise it will be good, and the display is excellent, but it falls down on build quality, and the keyboard has a rattle to it when you type that some people will find that irritating.