You know, it's a damn good question too... I ought to try for a less smart-ass answer.
I can't go for walkability; sort of for my smartass reasons above, but also because I've played plenty of courses on which a cart is the best way to play, but are also totally fun. I do think the BEST courses favor walking... I just can't put that as the #1 value.
It's a tough call. But put me down with the greens and green surrounds crowd. A course can be fantastic in views, shots to be played, angles, all that other stuff... but if the greens suck, it's just not gonna be very great. I say start with great greens and surrounds and then work from there.
TH