I think you have your years a little mixed up to make a fair comparison, but I still like the idea of this thread. Dolph Ziggler has only just now started his third real year as a WWE Superstar (I'm not counting his work in Spirit Squad). By 2006/7 Orton was already out of the Legend Killer gimmick, done with Evolution, and had multiple World title victories under his belt. To try and match Ziggler up with that is a bit ridiculous and unfair, in my opinion. Ironically enough, if you took Orton's career and looked at it in the same position as ZIggler is RIGHT NOW, he was about to win his first World Heavyweight title. Many believe Ziggler is on the verge of capturing the World title gold within the next a few months of WrestleMania (if not this weekend!), so that would actually put him right on track in your comparison with Orton! Nice observation, just off by about two years...
So let's compare the 2005 Randy Orton, about to win the World title from Chris Benoit and break out of Evolution...with modern day Dolph Ziggler, who for the second year in a row will battle for a World title at the Royal Rumble.
If we look at pure accomplishments, Orton has this by a landslide. It's nothing against Ziggler, but they gave Orton the greatest rookie push wrestling has EVER seen. Who else can say they were matched up will all the great legends from WWE's long history, and came out on the victorious end almost every single time? The Legend Killer gimmick was just pure brilliance, and without Orton would be nowhere near as popular as he is right now. Now, Ziggler has also done some impressive work. His feud last year with Edge was excellent, and his current work with CM Punk has been almost flawless. But unfortunately, Ziggler just hasn't been given that star treatment and insane push that Orton was granted upon his arrival.
As an in-ring worker, Ziggler wins the contest in my opinion. Trained by Lance Storm, one of wrestling's best trainers (and the guy that helped Jericho become as great as he is), he's probably the third best ring worker currently in WWE, after Punk and Jericho. Orton is great, and if we were comparing both men by today's standards it would be a much closer story. I know many would disagree and say Orton is mechanical and boring, but there is a lot to say about his intensity and how much of a reaction he draws from the crowd... Still, Ziggler takes the in-ring catagory.
In terms of mic ability, I also have to go with ZIggler. He just seems so natural at it, and while he's had his rough patches he's also worked through them and become one of my favorite promo guys to come around in a long time. Orton's early mic work was a bit awkward, and something Evolution definitely helped him with. But he's still just not naturally charismatic in his promo ability. In the ring, and with his look...totally! The Viper oozes charisma as a character, but he just doesn't do it for me when he opens his mouth.
So Ziggler's a better worker and promo man than 2005 Orton. But 2005 Orton had a way better gimmick and had already accomplished things ZIggler very well may never (like getting to face the Undertaker in the Cell)... I guess the only thing it comes down to is the original question the OP asked: who's the better heel? I think part of being a good heel is definitely your ring psychology, and largely your mic work. But at the end of the day it all comes down to the amount of heat you can draw. It's why managers like Vickie Guerrero, Teddy Hart, and Bobby Heenan are the greatest heels of all time. They draw such immense heat and that is what makes matches hot, which ultimately transitions into how we view wrestler's ring-work. It's true that if you are THAT good at the art of promo giving, you can manufacture that heel heat at the snap of your fingers. But Ziggler isn't at that level yet.
I have to go with Randy Orton as the better heel. Because of his gimmick, he was universally hated. Do you remember when he spit in Mick Foley's face, and FOley humbled himself and walked out of the building? I remember literally HATING Randy Orton at that point. I remember my brother's friend, who is quite a bit younger, got into wrestling during the Orton/Triple H feud. When he cuffed Triple H to the ropes and dropped STephanie, my brother's friend went NUTS! His rage at Orton was hilarious! When a fan can scream at the TV in anger and develop genuine emotion against a heel, THAT is the sign of a truly great performer. As much as I LOVE Dolph Ziggler...that's part of the problem. If he's a heel, I shouldn't love him. I shouldn't beg for him to come out and entertain me, I should hate his guts! Orton did that, and while a lot of it was the creative team and mentors like Triple H and Flair, some of that was genuinely Orton's character. Orton is just a much more natural heel, and it's the reason I can't truly buy into his current top face of Smackdown. I just want to see him kick somebody's head off....
2005, or 2012...I have to go with Randy Orton, as much as it pains me to do so.