I'm going against the consensus with Executive transportation and that's for a few reasons. I've been traveling to Vegas for quite some time and like to think I know the ins and outs and with that being said:
Executive shuttles are the most cost effective way of getting from the airport to your hotel.
Price Structure:
Strip Hotels: $6
Off-Strip Hotels: $7
Downtown Hotels: $9.50
A cab ride to just about any hotel on or around the strip will run you about $15, so if you're traveling by yourself, Executive shuttles are the way to do it. However, do not, I repeat do not purchase a round trip fare. These shuttle services are not to be used from your hotel to the airport. You will find yourself waiting and waiting for the shuttle and either making a late arrival check in or missing your flight altogether. You've been warned.