The Saints have matched up against 2 very strong offenses so far in the playoffs (Arizona and Minnesota) and they have done well enough to get them a ticket to Miami. The Saints also have had a very opportunistic defense all season, and that has continued into the playoffs (they forced 5 turnovers versus the Vikings). But the Saints are ranked 26th versus the pass, 25th in overall defense and 21st in points allowed. The Saints also have only one "big name" player,Darren Sharper, but as good as he is, he ain't as good as he once was (Sharper is now 34 years young). Despite their success versus Warner and Favre, Manning handles pressure as well as, if not better than, any quarterback in the league (ask the Jets), so the Saints won't be able to blitz him like they have Farve and Warner, and Manning doesn't make a ton of mistakes for defenses to capitalize on (ask the Ravens). Another thing to note, is that when the Saints struggled down the stretch it was because their defense didn't produce the turnovers they had the rest of the season. The Saints defense's conditioning and ability to disguise their defense will also be tested, as Manning loves to take his time up at the line of scrimmage diagnosing the other teams defense and making changes, but he will quick snap the ball if he sees the opposing defense trying to make personnel changes and get a free 5 yards.
The Colts defense, on the other hand, really hasn't faced a strong passing offense yet in the playoffs (New York Jets and Baltimore). Though both teams ran the ball well, the secondary has not faced the likes of Drew Brees. The Colts secondary statistically did not look strong last week, but Mark Sanchez's numbers from last week are not a great representation of how the Colts' secondary played. The Colts allowed 302 passing yards last week, but 80 of those yards came on a play-action bomb to Edwards, and 45 came in a play out of the "wild cat" formation which the Saints have not run much (if at all) this year. The Colts Defense did effectively shut down 2 of the best run offenses the last 2 weeks though (explaining the effectiveness of the play-action Touchdown), but as good as the Saints run offense is (ranked 6th during the regular season) it is not their biggest threat. What the Colts do well on defense is keep teams out of the endzone, the Colts are 8th in the league in point allowed. Mind you that is partially because Peyton Manning milks every second out of every snap of the ball, limiting the amount of time the Colts defense spends on the field. The Colts also have a quite opportunistic defense of their own when given the opportunity. And let us not forget about the twin terrors of Robert Mathis and Dwight Freeney who love to pin their ears back and make a B-line to the opposing teams Quarterback (at one point this season Freeney had sacks in atleast 7 consecutive games). The Colts defense is also very small, which normally puts them at a disadvantage, but the Saints offense is not a big 3-yards-and-a-cloud-of-dust bunch. They throw the ball a lot, which fits well with the Colts small, speedy defense.
This game very well could be a 45-42 game, but the defenses will make the difference, because both Manning (and comp.) and Brees (and comp.) are more than capable of lighting up the scoreboard at will. I might be a little bias being from Indiana (even more so because i am currently in Indianapolis) but I give the edge to Colts behind a good amount of pressure from Mathis and Freeney, and the most prepared Quarterback the league has ever seen.