Some notable gods and goddesses to play as are Aphrodite, Hel, Sylvanus, Cupid, Baron Samedi, and Ra. Each have very useful heals however I find that Hel, Aphrodite, and Ra have the strongest heals, with Hel having access to an area heal and a single target heal. An easy way to ensure the match lasts long enough and you have enough targets to heal is to play the arena game mode. Purchase the Rod of Asclepius as it gives a 15% healing boost as the first item, then move on to purchasing Soul Gem, which lets off a healing burst after hitting enemies with abilities. As long as you make sure to hit as many allies as possible with your AoE heal and your single target, then the achievement should pop relatively early into the game since you have so many allies to heal.