Gaelic Games correspondent Declan Bogue tackles all the battles in the big game both on and off the field.
Stefan Campbell v Odhran MacNiallais
With Armagh playing a two-man inside forward line of Jamie Clarke and Kyle Carragher, backed up by Tony Kernan and Kevin Dyas on the '50', Campbell and Aidan Forker will drop very deep.
While in defence against Meath, Forker was a wing-back, while Campbell drove forward from midfield. Pádraic Harnan originally marked him before going onto Tony Kernan, allowing Campbell to account for three points from play, with the Meath defence unsure of who to track his runs.
It's not something that would have escaped the attentions of Jim McGuinness, stickler for detail that he is, and in the crowded Donegal midfield MacNiallais would appear to be the player best suited to tracking runs. In scoring impressively against Antrim and Monaghan in Ulster, the Gaoth Dobhair man is a threat in possession. But Campbell is a mirror image for Armagh.
Charlie Vernon v Michael Murphy
Since being re-housed as a full-back, Charlie Vernon may have found his true vocation. An outstanding midfielder at college level, the Armagh Harps man took a while to get going for his county, having been placed at wing-forward and struggling at the start.
Facing the play he began this season shakily, getting an almighty roasting from Matthew Donnelly when Tyrone annihilated Armagh in the Dr McKenna Cup. Since then he has warmed to the task and was simply magnificent last weekend on Meath dangerman Michael Newman, rendering him scoreless. His size and physicality will be a good match for Murphy, who despite his obvious talent, just might be feeling the effects of having played a long season. Now that Donegal are back in Croke Park, he may be deployed closer to goal again.
Kevin Dyas v Karl Lacey
With Donegal liable to keep two sweepers in front of their full-back line, Lacey could be the man nominated to keep tabs on Kevin Dyas.
Tracking Stephen Gollogly in the Ulster final, Lacey was a constant outlet, hitting a point in the first half. It remains to be seen if he can produce the Herculean performances in Croke Park that landed him a well-deserved Player of the Year Award from 2012, but he has vital experience and never, ever concedes possession and has a talent to producing the kind of turnover or possession steals that excite a crowd.
Dyas' best hope is to use his youth and athleticism and see if he can in some way tire Lacey out. With Dyas the main link-man for Armagh's attack, his performance is crucial to their hopes.
Last year, Paul Grimley said in the wake of the Cavan defeat that his side had no time to develop an alternative gameplan to all-out attack.
This season would have told him that was untrue, as Armagh began working on their structured defence only a month before the Championship and it has made them competitive once again.
Getting defensive match-ups are crucial and James Morgan will go onto Paddy McBrearty, Andy Mallon will follow the out-of-form Colm McFadden and Charlie Vernon will take heart from how Sean McVeigh and Vinny Corey have kept Michael Murphy relatively quiet.
Brendan Donaghy will once again be entrusted with sweeping duties while, when they are on the ball, Andy Mallon, Mark Shields and Aaron Kernan should be encouraged to get forward at every opportunity.
If they can be enter the final quarter level, then some jitters may appear. And that's when Armagh must strike hard.
In capturing their third Ulster title in four years, there has almost been a sense that Donegal have been playing within themselves.
That may be because the team is evolving, with a strength in depth better than in previous years. They now have far more to throw at a team, such as holding Patrick McBrearty back in the Ulster final, only to send him on to pilfer three second half points.
Then, there is the development of Odhran MacNiallais, Ryan McHugh and the unpredictable talents of Darach O'Connor.
Neil McGee will go on Jamie Clarkr, his brother Eamonn will be on Kyle Carragher and they will retain Frank McGlynn and Paddy McGrath as sweepers.
Christy Toye, Neil Gallagher, Rory Kavanagh and Martin McElhinney will job-share their way through the 70-plus minutes, so midfield is of no concern. But they could be doing with Colm McFadden and Michael Murphy coming into a bit of scoring form.
The game in numbers...
Armagh beat Donegal by nine points in their last Championship meeting, the 2010 first round qualifier in Crossmaglen. A total of 12 Donegal players that day are still on their panel, but only seven of the Orchard County's panel remain.