I just returned from Vegas last week. I''ve been there many times.
The hotels most centrally located are: Bellagio, Paris, Bally's, Flamingo, Harrah's, Mirage and Caesar's. Of the three you've mentioned, I would choose Treasure Island. It is in the best location (IMHO) of the three and is a very nice hotel. I like the casino in Treasure Island. It is easy to navigate and somewhat calm. There is a tram between Treasure Island and the Mirage.
Treasure Island is across the street from the Venetian and the Canal Shoppes at the Venetian. You are walkable to the Wynn (gorgeous). Have their breakfast buffet - fantastic.
You are also walkable to the Forum Shops at Caeasar's Palace. You can explore Bellagio (also gorgeous). Paris is across the street from Bellagio. All of these hotels are fun to explore. They all have some fantastic restaurants and shopping abounds. Of course, you can gamble a little too
Are you planning to see a show? I saw LOVE at the Mirage (new Cirque show based on the music of the Beatles) and thought it was spectacular. I've also see Mystere, "O" and Ka! - all great.
You should go to all the hotel websites and register for e-mail promotions. I stayed in a huge lakeview suite at Bellagio last week for $299. I could have had a regular room for $149. It was a great deal.
The weather in February will be cool, but pleasant. Last week it was 100 degrees every day. In February, it will probably be in the high 60's, maybe 70 during the day, but it will cool off quite a bit in the evening. Rates could be good at that time.
If you have any questions, I will try to answer.
Have fun planning your trip!