Fiora's weaker than she was before, but is still a terror in the hands of those who know what they're doing.
Darius can completely dumpster a lane and take that advantage across the map as an advancing wall of free armourpen and true damage, and if not still scales kinda ok into lategame with his Noxian Might and bleed.
Vlad's recent rework made him more dependent on player skill than before, and he's less about mindlessly spamming your no-cost low-cd's; and more about managing your Crimson Rush stacks while properly trading with Tides of Blood. However, if you can accrue some skill with him, he's entirely worth it and has very few bad match ups (exceptions include
), while scaling super hard into lategame.
The three of them largely fulfill the same role on a team; kinda beefy top laners with mid-high damage but lack great utility (of the three Fiora has the most utility with her ult, then Darius with his AoE hook, then Vlad both before and after Rylai's).
Of course, I'm casting my vote you pick Vlad <3