Cowboy (guns/melee) will take you in a different direction than melee/unarmed. Unarmed unlocks much better up-close options than melee does. Cowboy wants high luck, finesse, better criticals, and to spaz on people with Chance's Knife, but I'd generally say that since Cowboy works well with some top-tier guns (Ranger Sequoia) but not really with top-tier melee weapons you're better off with Cowboy if Guns are your main and melee your 2nd, not vice versa.
Melee/unarmed - I like the 45 melee 100 unarmed split, which gives you Super Slam, Piercing Strike, Paralyzing Palm, Slayer. My version went low luck, heavy hands, Toughness x2, Rad Child, Stonewall, Adamantium Skeleton, so he's more of a bruiser than a ninja.