If your GF gives it the thumbs up, Osbsorne/Corydon area hands down if you are new to the city. It's "the" area for 20-30- something renters. Restaurants, bars, pubs, lounges, grocery, shopping, easy transport. All right by you. Densely populated, hip and lively.

Have heard good things about Assiniboine - it's downtown on the cusp of Osborne Village over the river but never lived there myself.

Downtown is going through a revitalization, and certain pockets are nice (Exchange District), but it will be a loooooong while before it has the everyday buzz and convenience of Osborne/Corydon in my opinion.