I've had mixed experiences with Ibis hotels in Europe, but this one is Prague is excellent. It's quite new and my room was clean and with a modern style. It had a double bed, TV, desk, phone and WiFi. Housekeeping gets a 10/10 for cleanliness.
The price is very reasonable and even lower if you book long in advance. It also includes a breakfast buffet with lots of choices.
It should be pointed out that it isn't really in the Old Town area, but a short walk from it. This is even better though because it means you are very close to the metro.