Fleet advantage: Very close. Mandos have more ships, Kun has better ships. However Basilisks are gonna change things a bit. I'd still give a slight advantage to MtU.
Actually, Mandalore the Indomitable said "you fight with antiques" to Ulic Qel-Droma. We know that the Mandalorians steal technology, improve upon them and use them for their ships, weapons and droids. Kun had Supremacy-class attack ships as the primary capitol ships in his fleet that are 550 metres in length, while the Mandos have the Kyramud-type battleship at 752 metres and Kandosii-type dreadnaught at 1360 metres as their primary capitol ships. The Kandosii is also packed with nuclear missles.
I'd say the Mandos have larger ships with more firepower, not more ships.
But the Krath have one very deadly weapon going for them that the Mandalorians don't have. They are willing to kamikaze their starfighters into enemy craft.