Chiang Mai
In 2012 we stayed at Yindee Stylish Guesthouse. It's nice but basic yet stylish boutique hotel in the old city. Fairly central location and inexpensive. Enjoyed our stay. Kind of hidden down a laneway. Laundry at the end of the road. Would consider staying here again if rooms available.
In 2014 I think we Hotwired it and ended up with the Suriwongse near Night Bazaar. It was looking a bit dated when we stayed but I think they may have remodeled. Big hotel. Came with breakfast. Location has some benefits being near the Night Bazaar but I think I liked staying closer to the old city. Many laundry options along Loi Kroh road. Not my first choice as there are other simpler and cheaper place but would consider staying here again.
In 2015 we stayed at the Imperial Mae Ping which is somewhat nearby the Suriwongse. Also a big hotel that came with breakfast. Kind of reminded me of the Suriwongse but slightly nicer. Waits for an elevator were annoying during the evening. Similarly, not my first choice but would consider staying here again.
I don't think you can go too wrong staying in the old city or just outside of it. It's a pretty walkable city and easy to get around by songthaew or tuktuk.
Siem Reap
In the spring of 2014, we stayed at the Banyon Boutique Hotel. Came with breakfast. Nice rooms. Small pool. Easy walking distance to pub street and all the restaurants and markets in the area. Would have stayed there again in the fall but the prices went up quite a bit and there were other options.
In the fall of 2014, we stayed at the Khmer Mansion Boutique Hotel. Came with breakfast. Nicer rooms and bigger pool. Just down the block from pub street. When we stayed there, the building next door was under construction and they got started early which was annoying. Would consider staying there again if no construction.
I suspect there's constant construction going on in Siem Reap with all the tourist dollars so maybe ask your prospective hotel if there's any construction going on nearby.
There seemed to be new boutique hotels sprouting up. They're nice and you can get a good deal on them.