We stayed at the Marriott Regents park for 10 days in December last year. The food was over priced, the room was just OK and the lobby was filled with smoke. On the plus side they had a nice pool, sauna and steam room.
This Marriott is about a 5 minute walk from the Swiss Cottage tube station. The area has a very relaxed feel to it. It's more of a middle to upper middle class area. Not a lot of resturants but there is a Marks & Spencer close by.
Once you're on the tube you can get to just about anyplace in 30ish minutes. Check on Tripadvisor for reviews of various hotels.
We used points for our stay and I think we could have been more in the center of things for the same amount of points. I might not stay at this hotel again, but if the price is right I would go back. I personaly like staying out of the touisty areas while on holiday. Breakfast with the locals is a great way to get a real feel for where you are.
I hope that helps.