I'd second a laptop. You can attach additional monitors to any decent laptop and all but the cheapest laptops these days are quite comparable to your average desktop. It's easier to get a better screen on a laptop than on a desktop monitor, too. The portability is very handy when it comes to working with other people, showing off demos at conferences or networking events, and moving when you feel you need a change of scenery to keep your motivation up.
I can recommend from experience a Samsung Series 8 or 9 (the Samsung laptops I've used are the best I've ever had), Lenovo Y Series (there's a sale on that right now and Lenovos are generally very well made), or a Dell XPS 13 or 15 (if I had need a new laptop myself, I'd go for a higher end XPS 13). Avoid ASUS; they heavily market so-called gaming laptops but they're... just dont'.
To support this advice, I would add up that checking up also Toshiba Satellite series is a must for consideration.
Never liked Toshibas which gives a "comforting" feel that you also pay Toshiba tax.
And no mobile CPU is match for desktop one, I'd rather go with a desktop and a cheap Win 8 tablet for presentation purposes ( Asus T200 perhaps )