If as you mentioned you're going to be using windows, then it doesn't make sense to spend all that money on the MacBook. I'd go for the Dell. I use Windows at work, and have a windows 10 machine and they're fine. I think in a number of ways windows 10 is superior to Yosemite.
There's many good reasons for buying a rMB (excluding individual specification comparisons) even if you are going to mainly run Windows:
If you are in the USA you have a complete on your doorstep apple support network of shops where you can walk-in and get help or service
Apple warranty more often than not works and exchange or replacement is often simpler
If you have an IPhone/IPAD you can flip back in to OSX to synch etc better than the windows icloud/Itunes
If you dual boot you are not excluded from any software
Legacy items (hardware/software) are not lost
You are not excluded or penalised in purchasing any phones/tablets etc as you can interface with the preferred OS
You can have the best trackpad which should be an important feature of a true portable system
You can opt for the styling and build quality of Apple, if it appeals to you
The Bad points (for some):
You have to buy Windows ($30-40)
You lose a minimum of 38Gig (for dual boot) as bootcamp will not select less
Some windows drivers specifically for Apple components may not be updated as often as native windows OEM's
Windows laptops still have more than one external port
Outside USA and some European Countries trying to sell used Macbooks is harder
Apple USB-C dongles are expensive