Question about 1 Din and 2 Din Decks
 

so im looking at buying a deck for my car its a 2003 Subaru Legacy GT and after looking at pioneer website and it shows my car being a 2 Din.

At first i was looking at getting the pioneer AVH-P5900DVD or the Alpine type one. but after seening this is it better for me to go for a 2 Din deck like the AVH-P6000DVD instead? how will the 1 Din deck look in a 2 Din Car?

It will look fine.
Some cars with a double din opening come with a single din radio.