In terms of bore and power, in technicality, a .44 magnum. No technicality, .45 ACP. Having a CCW makes it easier to transport both ammo and pistol to the range, I don't have to have the mag empty, grab the Deagle and go. But actually carrying it, like I said, .45 ACP
I wish they'd make a .50 Auto (Think .45 ACP style casing but holds a .50 round instead of a .45 round). I'd love to have a barrel and bushing set for a 1911 for a round like that. Not as powerful as .50 AE and similar to the .45 ACP in performance? Nice. It would be useful as an SD round for those that want max caliber. Not that it would be any better, but it would be a different flavor.