Aitor's place is even better than the pictures! It is super clean and very stylishly decorated. The apartment is in a great location a very short walk (5mins) from the old town. We actually liked being slightly away from the old town as it was a little bit calmer and less touristy. There in a pintxos restaurant right around the corner (full of local people) where we decided to go one evening instead of the old town and it was buzzing, as well as some great bars on the corner too.
The beds were very very comfy and the shower was very good too. It is a comfy, cosy space that would accommodate four people very comfortably.
We got the bus from Bilbao airport, and the bus terminal is only a 10minute walk away so this was very convenient. For those visiting the city it might also be useful to know that you can store luggage at the bus terminal for only 5euro a day - we found this really useful as we had a late flight home and didn't want to carry our bags around with us all day. We could fit two bags in one locker so this was a great solution for us.