Well rigocampos, it depends on how long you will stay in Las Vegas, what time of year it is, and how much money you are willing to spend.
If you don't have much to spend and want to stay a couple of days, try Bally's or Harrah's hotels. Their rooms aren't too bad and they are fairly low priced.
If you have one or two thousand to spend, you can stay at the Palazzo, for under two-hundred a night most of the time, and their rooms are great; all suites with big screen TV's and nice washrooms.
I've heard the Bellagio and Caesars Palace hotels are great too, but they may be a bit more pricey to stay at.
If you are use to temperatures over 100 degrees, visit Las Vegas during the summer months; June to August. If not, you can visit any other month and the heat is at least bearable.
I like visiting between February to May and late September to late November, when the temperatures are between 65 degrees to 90 degrees.
Las Vegas is in the desert, so that means at night time the temperatures can drop from 20 to 30 degrees at night. If it's 90 degrees during the day, it can get down to 60 or 70 degrees at night.
Bring short and long sleve shirts, shorts, pants and a coat or two, you don't know when the weather will change.
Dress for the Las Vegas weather and your time will be more enjoyable while visiting.