I've played both builds a lot, and right now I feel that Kaiser is the superior build to Black Garden. Black Garden builds have a bit more utility because it's better able to search what it needs with Terraforming/Tenki, but I also found it too combo-centric and easier to combat with commonly played cards like Vanity.
Black Garden versions are cool when they go off without hitch, but Kaiser/Vanity builds dominate the popular matchups imo. Kaiser/Vanity play well against the meta and usually result in easy wins in a lot of matchups like Drags and Evilswarms. Garden has a slightly better matchup against Spellbooks because you can play Garden over Tower, but that's about it.
As for the Kaiser builds, I've gotten a lot of good use out of Horn. It's effective both when you open well, and when you open up not so well. If you're going well, the opponent tends to turtle up because of a lack of options. This allows free +'s each turn as you build defensive resources. If you open not so well, you can still make use of Turtle/Quil in an offensive manner before they hit grave. It's generally unexpected, because they know you can't Crane onto Turtle/Quil and you normally wouldn't want to waste a Lance in that situation. It buys time until you hit on Yamato.
Also, a tech card I'm trying but not completely sold on is Vivvit Knight. I find it to be more versatile than Lance and it can work hand-in-hand with Turtle. It can save Yamato from attacks, as well as monster effects (i.e. a wasted Big-Eye). He's also Beast-Warrior and is searchable protection via Tenki. It might be something worth trying out for you.