Reward-by-item quick reference (which bosses give the most of each): SPEED-UPS: Cerberus, Pan, Ymir, Griffin, Witch, Warlord, Hydra. RESOURCES: Ymir (best), Witch, Warlord, Royal Thief. MATERIALS: Viking, Bayard. GOLD: Viking (Hard+), Bayard. MEDAL: Viking. REFINING STONE: Ymir, Pan, Witch, Warlord, Golem, Lava Turtle, Viking. RESEARCH STONE: Viking (Hard+), Witch, Warlord, Hydra L3-4, Golem, Lava Turtle. SPIRITUAL BEAST EXP: normal bosses Werewolf L5+ and event bosses (best value Minotaur, Ymir1, Witch1, Warlord1, Golem1, Lava Turtle1). GENERAL/MONARCH EXP + STAMINA: Hydra (drops chips in bulk -> spin Wheel of Fortune for stamina). RUNESTONE: Pan L4+. TACTIC SCROLL: Pan L4+, Aglaope. BLAZON: Sphinx. SOURCE OF LIFE: Sphinx L4+. BLOOD OF ARES: event boss L3+ or normal boss L11+ (up to 3/day). BLOOD CRYSTAL: B14 Behemoth+ normal bosses, or event bosses of >=200M power (Warlord/Witch/Golem/Lava Turtle/Ymir/Pan/Hydra/Sphinx/Cerberus/Bayard). CRIMSON CRYSTAL / AWAKENING STONE (beast smelt): from Garuda and World Boss (by damage, not drops). Every kill also yields a level-tagged Boss Monster Chest (materials, medals, gold, EXP) + Prestige + Alliance points.
Original research source: Evony Guide Wiki