Hello lovely Marie ---- Majahuitas on a Groupon? Hmmm. How intriguing. I've only done day trips there, but I see what you mean.
You will need to be in the middle of things, for just one night. The Sheraton is fine but I wouldn't really call it a 4-star. Seemed more like a 3-plus. Doesn't seem to fit what you are describing, unless it's done a major upgrade since I stayed there. Also, it's a bit north from activities and exploring town --- it would also not be convenient to get back there during the day if you wanted to get out in the morning and then go back out later.
What day of the week would be this one night? If you want to be in the middle of things (you don't have time to be out of town), I'd recommend Casa Isabel, Playa Los Arcos, Villa Premiere or a range of other B&B type options within walking distance.
Someplace where you don't have to spend your time in transit? Did you want a romantic place? Did you want a place where you can hit the ground running and be at your choice of a dozen different restaurants in a short walk? How long will your one day be and what type of shopping would you like to do? --- crafts, clothes, etc?
Have fun, but do try to stay closer than the Sheraton if possible being that it's just one night.
PS to edit: Funny. Teduardo and I were writing at the same time and said something very similar. Hope that helps, hearing it twice.
Edited: 6:04 pm, January 21, 2013