Similar to Alden, she is somewhat of a Jagen early on. Her dodge tanking is super effective early game, though does start to fall off in the mid game when the enemies gain additional accuracy. Having access to a heal allies places her a little higher in this tier than Gwyn, but mid-late game she will still end up buffing more than healing.
Early on, Valeria is a "weak," speedy unit. She finds a surprising amount of success in both her base class, Nightblade, as well as Gallant.
Nightblade - While this class on Valeria only totes a 30% strength growth, the devs try to justify it by giving her a 15% increase to power at full hp. Yeah, it doesn't make up for it. They did however, give her a lot of speed at a whopping 65%. In Nightblade she can buff herself/allies with more speed or debuff allies with poison, reducing all of their stats.
Gallant - In this class, Valeria gains a truly decent blend of stats, primarily power at 50% and speed at a respectable 40%. Using the Overpower skill was something I neglected on my first few playthroughs, but it is deceptively strong. Valeria really appreciates a bit of Elixir love in the form of both 1 Strength and 1 Speed elixir and is a decent candidate for the Bloodied Ring early on to help her one round foes in demonic.
Seeker - Valeria can make use of this class but it feels suboptimal in every way.
Devoted - This class really needs a buff. Hemorrhage costs 10 too much mana and Spinning Blade needs to apply Heavy/Severe Block and have it's mana cost reduced by 5. Ridiculous.
Champion - If you want to make Valeria a Champion, you should decide early on. Level her as a Gallant and then before you promote her, go Nightblade for her self speed buff. This will ensure Valeria can hit hard and double which is not something many Champions can do. Due to her personal passive, you want to keep her topped up on hp. This is rather hard to do; however, use of Nightblade's passive along with the Victorious ring will make this easier.
Reaper - Reaper kind of has a cookie cutter build. You either go into Gallant for it's passive and strong buffs, or you go into Seeker for its selfish buffs but Gallant is almost always a better choice. Due to Valeria's high Mastery, I recommend Gallant for the massive Call to Arms buff. Use either the Lava or Mystic Ring as well as the Destiny Ring. Make sure you stay out of combat while Destiny Ring is building its crit and pop your banner buffs from safety in the meantime.
Ellisant - Similar to the Reaper, you want to be a buff bot. You can go Nightblade or Gallant, both the speed and the power buffs are great, though the speed buffs are a little more limited as you can only buff one ally. If you can get some early kills, the +1 power from the Crusader Rune and Competitor Ring will put in some work for Valeria.
Ancarant - Valeria is great as a Nightblade - Ancarant ... not so much. There's not really much she can't double though so if you do decide to go all in on her, the Advantage Ring lets her ignore a percentage of the enemy's defense/fortitude based on her Mastery. Additionally, Valeria will finally have access to being a dodge tank AND having a way to heal herself through Glaive Toss. Moonlight Beacon is also extremely strong.