Let me answer this question for you since it seems nobody else actually has.

First off go with the Shadow Hearts series because the fighting system is clever and the story line is quite captivating, just play them in order 1-3.

Next, move onto either Grandia 3 or Radiata stories, here's how you decide; if in the past you have played Grandia(1,2 or extreme)and loved it's awesome battle system then go with that first, it's a short game anyway, if you haven't played it then you might as well skip it cause the story can be dull and the fighting, while cool, does not save that game from being bleh.

After you beat those games move onto playing ShinMmegami Tensei:Devil summoner but at the same time start playing Atelier Iris in order from 1-3, this way if you get bored with Shin Megami, which is highly possible you still have something else to do.

You asked for my oppinion on what order you should play these games and that's what I think based on the fact that I've played all of them; I hope this helps.