In Torres del Paine you have very limited options to stay. If you have the time and physical ability to walk around and stay in Torres for 4 or 5 days, walk around with a tent or sleep in a refugee.

If you only have limited time, and don't want to spend 300 US dollars per night, you only have 1 option. Posada Rio Serrano, next to the entrance of the park. Don't expect anything for the 85 US dollars you pay. The double room we booked was nothing more than a very little room, with a bunk bed. Not a romantic get away! The shared shower and toilet were both very basic.
We hated it so much that we only stayed 2 nights of the 3 we payed for, and spend the last night 280 dollars in the overpriced but luxury hosteria las torres, also in the park.

The only good thing about the posada is the restaurant. This restaurant was excellent. The (simple) food they prepared was very tastefull, and the waiters were very friendly and polite.

We decided to book this hotel (4 nights) after reading lot of reviews about Park accomodations (Explora was too expensive for our budget).
We definetly think Serrano was pretty good if you have your own car (4 wheel) and if you like to drive 2/3 hours a day.

Positive: food - rooms - organize all excursions (included horse-riding or zodiac-navigation to Balmaceda Glacier)

Negative: location far from the park (half an hour drive to main attractions (Glaciar Grey, jetty to Valle Frances), expensive for dinner and excursions.

Torres del Paine is very beatiful: we visited Valle Frances, Rio Pingo (no way to see huemules), Glaciar Grey and drove all the park in just one day (we've seen guanacos, nandu, condor, foxes)

What a relief it was to check-in at the Rio Serrano after two nights in sub-standard accommodation at the Hosteria Las Torres. The rooms were large and all had wonderful views of the mountains. The food was very good with a fixed price meal every night with several choices: it seemed a little expensive but the tax is deducted from the price if you pay in dollars when you check out. The hotel is quite new and has been carefully planned with large public areas away from the rooms. There is a nice terrace where you can sit and watch the changing sky and light over Torres del Paine.
You do need transport at this hotel to get back into the park. The excursions are expensive but if you are a small group you can haggle with the hotel over the quoted per person prices. An important point: the hotel is just outside the park so you must keep your park entry ticket if you are going back in again (it is valid for 3 days). Our guide did not give us ours and we had trouble persuading them that we had already paid when we wanted to go back in.

I was pleasantly surprised by how nice this hotel was. It's pretty new, which helps. The public areas and guest rooms were quite beautiful and luxurious, and the staff were reasonably helpful. It's just outside the park boundaries, but every room has a fantastic view of the mountains of the national park. There are a few hotels in the park with more convenient locations, but this one was pretty good location-wise. Like everywhere else in or near the national park, however, it's very expensive. We also stayed several nights at Hosteria Las Torres, and, unless you're doing the Mirador Las Torres hike (for which the Hosteria Las Torres is much more conveniently located), Rio Serrano was about as convenient for most of the park, and was considerably nicer for about the same price.