Asuna makes a good waifu, she is fine as a character as well but there is no promotion and I don't like her so much.
On the other hand, I don't think I learned anything special about 2B either. Voting for 2B, mostly because of her looks

.
Asuna is a bland character from a bland anime everyone has seen. You could talk what little there is to talk about her without really spoiling anyone. With 2b there is plenty to talk about but it gets somewhat difficult to do so Without giving massive game spoilers.
Anyways, i am going to try to explain about her without spoiling this marvelous game. The games setting is basically the year 11000. Humanity has retreated to the moon due to an alien invasion 8000 or so years ago. The alien army is made out of machines. The force that stayed behind to fight them is made out of Androids. 2b is a battle type android. The game revolves around the exploits and experiences of 2b and 9s, a male scanner type.
The two of them specifically work for yorha, an elite android division. Yorha through the game gives them missions. Most of them revolve around destroying threats or gathering intelligence on machines which have begun acting in unusual manner. So basically tue setting is a couple of elite androids fighting a thousand year old war that got weird.
Personality wise 2b appears to be all business. She does her job quickly, efficiently and beautifully. She has a fun side as she is also shown teasing others occasionally but that doesn't show too often. The game largely revolves around her interaction with 9s and the strange and disturbing individuals she meets during her quest. And also, her guilt...