Vladimir has had really weak keystones for awhile. Thunderlords is nice, but it's pretty hard to proc early on, and most Vlad builds don't have enough AP to make use of the single target burst provided by it. Deathfire is nice as well, but it doesn't feel incredibly impactful. It's also a liability if you're trying to harass someone under tower.
Stormriders is supposedly good, but I haven't tested much with it. Vlad has the damage to use it, but it's still arguable. I've heard SotA is the Korean meta, it's been testing well also. Gives good stats, minor sustain mid-game. It's also viable.
Windspeakers is what I personally use. I've won games because of this keystone before, and I'm basically stuck on it. Between Windspeakers, Spirit Visage, and Runic Armor, you get nice sustain mid-late game. It's less noticeable early game though.