That's not how basic attack bonuses work, for neither god's angels or hans. God's angels, after the first attack, transforms your "attack" from a basic attack into its own unique attack. Hans actually increases your basic attack hit count. For god's angels, equipping +1 basic attack gear does nothing after the first attack. For han's it just adds 1 attack so +11 hits > +12 hits. You could get +16 hits with 4 pumpkin rings and kuti covenant though. As for which is better, it depends. Hans does 4x attack against 2x defense per hit while gods angel does 3x/2x. However, gods angel uses certain hit so it ignores physical damage resistance (which like half the bosses in the later stages of the game have 30-50%) but that also means it doesn't benefit from break/hard break. Unless you meant extra actions (e.g. black rabbit ring) then just ignore this.
The only trick to the horses is to just tank it. Their fight is scripted to stun you before you can act, ignoring luck and resistance, and their first attack does huge defense ignoring damage, around 150k at diff 0 (unless they crit with their 70% crit rate but at least you can get crit immunity pretty easily) and inflicts stun again, this time ignoring only luck. So if you have more hp than that you will survive their first hit. You can also get physical resistance from bunker shield or iron rings. Also stun resist, or lots of luck, helps since all their attacks inflict stun.
Black slash is one of the ultimate skills from bs 1 found in deep chaos dungeon from the floating books.