There’s no best hero class, it depends on your play style. Most used one’s are death knight, and archer.
Best team at your level is one that include a soul generator troop in it. At your level valk is the best option, and pair her with some blue troops that deal damage - so you can use the blue mana you will generate from valks spell.
Later on when you find it, the Dragon soul is also a great soul collecting troop, and you can use it instead of valk (preferably in a full Dragon team).
A tip for start? Find a strong guild. Players in there will help you and rewards from guild will be more than half of all your resources.
I only used a hero until I my level was high enough that my hero wasn’t needed anymore. Maybe your level, probably earlier. Kingdom and troop type bonus were of higher value then, best both.
When I was little I used Goblin teams, later I switched to Undead and used those until I finally got 4 Dragons from Dragon Claw together (for pvp). I still used the Undead team for soul farming. Took me long to finally get Dragon Soul for a better soul farming team. So long Banshee, Wight, Flesh Golem and another one I can’t remember anymore (Undead) had to farm.
I’m lvl 570 now and never use my hero (now even kingdom/trooptype bonuses aren’t of value anymore). Sometimes I test but decide against one again.
But hero weapons I often see in pvp are: Creeping Death (Neco class weapon), Prismatic Orb and Black Manacles.
Did you join a guild? That’s the most important in this game. An, at least, semi-active guild. Join randomly one and check for the activity (guild wars and rooster in guild menu) and join one until you have one that does spend gold in the tasks. Boosts you so fast, esp diamonds which you’ll need for farming armor and later to trade for souls.