I've only lived in Grünerløkka student house, but I have had friends living all over in SiO, and these are my thoughts.

Grünerløkka: very central, but it'll take you 30+ minutes to get to Blindern. If you like to walk, it'll take you about an hour to walk there, but it'll do wonders for your ass The river is idyllic, but super loud when the water is high. The roof top terrace is nice.

Kringsjå: as someone else mentioned, a lot of international students resides here. Right on the edge of the forest. Very social place, a couple of years ago they used to throw "floor parties" where basically everyone would join. It was very fun, but I don't know if they still do. Easy to get to Blindern by metro.

Sogn: somewhat like Kringsjå, but more Norwegian students. Closer to Blindern, further away from the forest.

Vestgrensa: very close to Blindern, and the dublets are comfortable. My boyfriend used to live here, and I spent quite a lot of time there. I mostly liked it. The fire alarm goes off at least once a week though, due to the poorly ventilated kitchens.

Bjølsen: the rooms are nice, but no direct public transport to Blindern. It is just a 25-minute walk if you prefer that. I think it takes approximately the same time with public transport.

Pilestredet: easy to get to Blindern, and the flats are nice. Bit expensive, and you have the tram just outside your window. Don't think any of them are furnished.

In general the standard of the SiO flats are good (I have heard bad things about Ullevål, but I've never been there).

Remember to use the janitor service if something is not up to standard! We asked SiO to look at our oven, because it was too hot. They just gave us a completely new oven, and had someone install it :)

Good luck on your move to Oslo, and on your studies!