Kuan Seo was a really nice guesthouse. I stayed in one of the rooms upstairs (I think there are a few rooms downstairs, but I never saw them) and it was great. The room comes with fan, AC and ensuite bathroom with hot shower. The walls are bit thin, but I think that's pretty common in guesthouses in Luan Prabang.
The staff there are also really great (however, their English is not the best). Our shower broke the first day we were there and they did their best to fix it. When they couldn't they called a repair guy right away. Unfortunately it was Saturday (which is like their Sunday as far as work is concerned) and they couldn't get a hold of him. In the mean time, there was another shower we could use. The next day, at 9:00 am sharp, the guy was there and fixed it in like 5 minutes. Unfortunately, we had already booked a different room somewhere else as we were sort of expecting the "it'll be fixed tomorrow" run-around, but they were totally on top of it. I felt bad for making such a negative assumption but the host was really gracious and always said "hi" to us with a smile when we passed him on the street afterwards.
No WIFI. But Joma Cafe is just down the road and their connection is pretty good by Laos standards.
Tip: It's tough finding a decent and cheap in Luang Prabang during high season. Most places are always full and won't take bookings because boat/bus-loads of people show up daily. My advice: call ahead the night before, or the morning of your arrival. We did that for Suan Keo and they held the room for us.