I am no expert on this game but I have found out that there is no true party but you will need different set ups for different battles. The tier that LordRaven shows is just one that he feels are the best and as you can see that there are that think different, so that beening it depends on what works for you and the type of battle you are facing. You have a good start and some strong tanks plus strong assassin. I would work on builting some support such as the Freya and try to get a Shalana. Use you lower one to built you main team. I myself have about 6 teams that I use. Elements also help when they are all the same in your team.
Well hope this helped but like I said I am still learning myself so good luck and hope you enjoy the game.