Aria or Aqua?
 

Hello, I am currently trying to find a birthday present for my sister who says that she quite enjoys the type of easygoing plot that this group of series has. My question is, should I get her the first volume of Aria, or the first volume of Aqua? Or should I just get another volume of either of these series? Thanks!

EDIT: Basically, which series is better written and drawn? Which series should I spend money on, if I can only get one volume?

I'd start with Aqua since it's where the story begins. It's fairly episodic but still jumping to Aria directly, you'd be skipping the character introductions and quite a bit of background knowledge.

Meaning, Aqua is a prequel to Aria. So if you feel the beginning/introduction isn't too important, you can go ahead with Aria. If not, Aqua. Haven't read either Aqua or Aria yet so i can't tell you if there is a big difference between the two, however.

Well not so much a prequel. Aria anime is based on both Aqua and Aria mangas. In my opinion Aria vol. 1 could have just as well been Aqua vol. 3 and should be taken as one.