The first two Ultimas were never released to Amiga. So instead I would play Commodore 64 versions:
Ultima I: The First Age of Darkness
Ultima II: The Revenge of the Enchantress!

These Amigas have been released or converted to Amiga:
Ultima III: Exodus
Ultima IV: Quest Of The Avatar
Ultima V: Warriors Of Destiny
Ultima VI: The False Prophet
Ultima VII Part 1: The Black Gate & Forge Of Virtue
Ultima VII Part 2: Serpent Isle & The Silver Seed