My starter was war princess and I don't regret it, I got another from gems and upgraded after finding a rainbow map in guild and had a decent mono green team for a long time. I was able to build a healer from guild shop cards and have seen many healer cards pass by since having 6 star white healer. Floral saintess I obtained from a gem drop and have never used, it is really bad, someone is much better with a diff starter and using a friends healer because tons of people have healers you can friend with.
As for the best starter? It is all luck, it depends on your other cards. Agni is great but if you don't have other decent red cards it doesn't have the same value. Unfortunatly all this talk of best starter card rarely gets to the player because they don't start reading the forums until they are already decently into the game and pass the point of wanting to start over.