Pirlo is one of the most precise passers in the world, you giving Iniesta dribbling is just nitpicking at attributes. I could easily give Pirlo long range passing, and free kick/ set piece ability but as Chem said this is besides the point.
Barcelona is a system club and it makes ranking individuals a bit harder than usual. Iniesta has always been more of a secondary player for me. I think he is very good, but he does not merit all of the praise that he gets from everyone. Some people actually think he is better than Xavi, when he has been riding on his coattails for most of his career. Sure, he has shown up in some big and important matches but his overall contribution and end product leaves much to be desired.
Another thing you guys need to look into is their respective supporting cast. Pirlo has had much less of one at both club/international level and still puts up better numbers than Iniesta. He has also been able to do it for different clubs, while Iniesta has only been at one his whole career. Pirlo was unfortunately and unjustly ignored post Calciopoli, but his performance at the 2006 World Cup was much more influential than anything Iniesta has done for Spain. People tend to forget how much Xavi was ignored before Barcelona became so popular.
I place Pirlo and Xavi miles ahead of Iniesta and none of them in a top 10 or 20 list. I'm not liking this new trend of having to throw every recent Barcelona player into a discussion of greatest player of all time.
Dribbling nitpicking? I think not. This is a key part of Iniesta's game, that burst past a couple of players that can break a line of a team's defence. I'm thinking of goals like the ones Xavi and Messi scored against Arsenal a couple of years ago - all created by Iniesta's dribbling.
I think every truly great club/team has a great collective system - sure the system is a big part of what makes Barca/Spain great - but at some point, you have to credit the players who perform in that system for making it work.
I think you vastly underrate the level of Pirlo's supporting cast. For Milan: Stam, Cafu, Rui Costa, Seedorff, Gattuso, Kaka, Shevchenko, Crespo, Maldini, Nesta. For Italy: Maldini, Gattuso, Nesta again and add on Cannovaro, Totti, Del Piero, Buffon. I'm not pretending it's as strong as Iniesta's supporting cast (I think Milan runs Barca somewhat close in individual skill, Italy 06 less so), but let's not pretend Pirlo had a bunch of mugs to work with. I think the fact Pirlo changed teams and won something at Juve is to his credit, but I don't think it's a reason to knock anyone who stays at a club for very long either.
Can you explain what you mean by better "numbers" from Pirlo? He certainly doesn't score as much as Iniesta, and I can't imagine him assisting more from his deeper position. In any case, I think Iniesta is an example of a player who's value goes beyond pure numbers. Even though he probably doesn't score as much as he could, you can't sum up what he brings to the team by pure baseball style statistics. The guy just brings it when it really counts, both in the Champions League and internationally. I really don't see what justification you have for claiming he's some chancer riding off Xavi's coattails.
No need to exaggerate my position about this, btw. I'm not asking for Dani Alves or Pedro to be put in the top 10. I just think the 3 true greats of these two teams deserve to be recognised. It's not like it's a one season wonder - I'm not asking Wesley Sneijder to be put up high. This consistent level of domination has gone on for 5 years now (and as you say, Xavi has credentials from before then too), and it's these guys who are the centre of these teams. I agree Xavi should be the higher of the two, as he kinda embodies that tiki taki ultra possession of the ball with his regular 100+ passes a game, but I also think you shouldn't separate him and Iniesta too much, since they've worked in tandem so much for their teams.