You're getting a lot of feedback from more "wide-ski-oriented" skiers, so let me balance it out. I particularly disagree with Shredhead:
Go fatter and longer. 180+ length and 88+width. You can ski groomers on anything. Where do you want to rip the most, powder or groomers?
Yes, you can "ski" groomed snow on anything. But isn't the point to enjoy it, not just get down it? I think that it is no coincidence that fat-ski afficionados tend to proclaim their distaste for groomed snow, or anything not deep and soft. I wouldn't like it either on those skis!
And what about when it gets harder, windblown, bulletproof, or otherwise "loud"? That's been the prevailing snow conditions in much of Colorado for the last couple weeks--and the east is no stranger to it either! I met a friend of mine in the grocery store the other day--a friend who is a former "big-mountain" competitor and who loves to preach the virtues of fat skis. I don't know how many times he's tried to convince me that they "ski great" in all conditions, and are super-versatile, and so on. "Have you been skiing much lately?" I asked him. "No," he said, "I don't like hard snow."
While it does take some technique and skill (what of value doesn't?), you can certainly ski (even "rip" on) narrower skis in deep and soft snow. Indeed, groomed snow and powder are the two easiest conditions to ski, and you can do fine with just about any type of ski--once you learn. To me, the test of a ski is how it performs on--or in--challenging conditions. I would much rather ski powder on a narrow ski than hard snow--or even groomed snow--on a fat ski.
So, if you want to enjoy--not just "ski"--all conditions, I'd steer you toward a ski with a waist between 72 and 88 mm for that one, all-around ski. And personally, I'd go much closer to the narrower end of that range.
If you can find them--and afford them--you cannot go wrong with the new line of Hart skis. In that line, the two I'd lean toward are the Pulse (77mm waist) or the Twisted Twin (86). They are both hand-built laminated skis. The Pulse has a deeper sidecut, and is generally my preference. Hart describes the Twisted Twin as an "all-mountain twin-tip." It can carve decent turns on groomed snow, but really comes alive in softer snow, as well as freestyle maneuvers--half pipe, switch, and such (I wouldn't take such a fine ski near a rail, though--or any ski if you want the edges to work).
Reading between the lines, you've probably figured out my top recommendation: Hart Pulse! Around here, it's become an overwhelming favorite of instructors, who need a ski they can do anything on, anywhere. It has proven itself well in our certification exams, which include skiing the entire spectrum of speeds, movement patterns, turn shapes, conditions, and terrain--from groomed to steep off-piste and bumps. I prefer a still narrower ski (race ski) on real ice, but the Pulse has impressed me even there.