Mandalorian Keldabe because it's big, it's mean, it's heavily armed, armored, and shielded, and meant for combat. This thing could go toe-to-toe with a Star Destroyer and win.
Keldabes are excellent, although they technically aren't Mandalorian, they were just manufactured by Mandal Hypernautics
As for me? I'll take a Mandalorian Kandosii class dreadnaught. It not only is made for space combat, it also holds a ton of ground forces, ready to conquer more systems for Mandalore! Or you can just nuke the shit out of a planet that's too hard to take
True, but by modern standards, the Kandosii isn't that large anymore. Sure you could fix that by up-sizing the hull, but still. The Kandosii is a nice ship, but I prefer the feel of the more modern Keldabe.
Now, if I could go with a costom design... I'd go with either my Marauder Corps Marauder-class Star Dreadnought, or - for a more Star Wars feel - my Merger Star Wars Design, the Predator-class Warship. It's a merger design of four classes of Star Destroyer - combining traits of the Interdictor Cruiser, the Imperator Star Destroyer, the Harrower Star Destroyer, and the Victory Cruiser.
Dammit, now I wanna show it off. Anyone wanna see it?