It depends where you find yourself in life when you start your PhD. Personally, I think doing your PhD as a full-time student/part-time employee is the least stressful option, usually because you don't have things like rent, cars, credit cards, etc. to pay (the usual stuff that comes with fully 'adult' life). I started out as such, but needed to take on full-time employment during my final year, which was pure hell.
However, the latter is doable - I just graduated and am writing an ebook on the experience to support other PhD candidates in the same position. Check it out at www.survivingyourphd.strikingly.com .