3000 Grand - big building, fairly nice, has a gym and outdoor pool, more expensive than others around
The Imperial - directly across from the school, decent, DMU wireless available in building
There's also an older set of brick buildings that I can't remember the name of for the life of me right across from the school (next to the Imperial) that were fair, and probably the lowest price of the three.
I basically looked at those three and went with 3000 Grand, but many students live in each.
As far as a roommate, it can certainly be great if you get along well...study partner, company, and cuts down on costs. But getting along is the key.
I'm sure somebody in first or second year can provide more info...I'm a 4th year who's lived in Ankeny the last three years.