For spellcasting, scholar blood is your best bet giving you that sweet 14%-20% spell power boost right from the start and some nice cooldown resets once you get higher quality. Make sure you're hitting that 90-100% quality mark, since that's when things get really interesting with the reset chances and life leech. If you're going melee though, you've got options depending on what you're after

Warrior blood is straight-up physical damage and shield procs, while brute gives you that tanky sustain with health and lifesteal. Rogue's pretty fun too if you like landing those big crits and zipping around. The real magic happens when you start mixing blood types later on, like scholar with corrupted for a more survivable caster, or rogue with illusion if you want those sneaky critical hits

Good to know that spell builds work best when you stack magic power gear with cooldown stuff, and melee builds want physical power with defensive stats. Maybe interesting - mixing rogue with illusion spells lets you pull off some pretty nasty stealth-crit combos, and scholar with unholy magic means you can keep summoning minions basically forever if you time it right