Wynne is the base healer of the game. She is a mage you meet at Ostigar but you can't recruit her until you visit the Circle of Magi Tower after finishing Lothring. She is the Spirit Healer subclass.
My biggest issue with Morrigan is that she is already specced into the subclass Shapeshifter, which means you lose out a lot if you want her to be a pure caster and ignore the alternate forms, plus having a subclass already means you can't get another good subclass like Spirit Healer or Blood Mage until lvl14. It seems Spirit Healer and Blood Mage are the best combo since you can have the healer not only heal with mana, but use up her own life to heal once they run low and drain life to regain it in order to heal further, it would stop the near constant potion chugging you have to do with your healers as they buff, heal, regenerate, etc... I ended up not doing that combination with my healer, Wynne, because I didn't feel it fit with her character, and character is a big thing for me. Morrigan is going to be another story if I get a way to respec her, since I am going to give her Spirit Healer/Blood Mage with points in Death Magic, Blood Magic, etc... talk about a wicked cleric.
I think the game really should have a respec option, something you can use on the companions in order to rebuild them completely from scratch. Make it even require that they have to really like you and are willing to change their life a bit in order to help the greater good/evil or whatever you are doing, and would also require money in fees for retraining.
My character I just finished the game with I played as a warrior-born with the guile of a noble, basically very cunning and persuasive while being great with duel weapons and the ability to rally others with the champion subclass. I don't plan to play again for awhile, but I already got ideas of what I want to do when I replay, all the choices I will do differently. My main ideas are a human arcane warrior with blood magic being my second subclass, Morrigan as my healer, Shale as my brute, and Dog as my damage.
My other idea is to challenge myself with a Dalish or City Elf Duelist/Ranger that would work mostly with Zhevren (Assassin/Duelist), Leiliana (Bard/Assassin), and Morrigan (Because I need a healer with all the squishy). I don't have much if any desire to play a dwarf, though I might make them anyways for the Origin stories.
Yes I know I could always just turn up the difficulty setting, but I am a person that would require a challenge with unorthodox companion builds then min/maxing as much as I can just to survive the horrible onslaught of beefed up monsters.