Depends on whether you want to get to Vegas the same day you depart.
I have had a series of problems with America West, which is why I don't fly them anymore. The problems were all mechanical related, and they have such a thin fleet (and such few mechanics) that timely resolution was an issue each time.
If you have to change planes in Phoenix, and you probably will, just plan on spending the night because you probably will miss your connection.
The last time I flew them, I intentionally booked a direct flight from Atlanta to LV, with a stopover in Phoenix (but continuing to Vegas on the same plane). I figured that this way, when we were late to Phoenix, we would already be on the "connecting" plane so I wouldn't miss it. Sure enough, we were about 1 1/2 hours late into Phoenix. Everyone else was panicked, but about a dozen of us stayed on the plane for the flight to Vegas. Unfortunately, American West decided at the last minute because of a bunch of late arrivals to change the flight number and destination for our plane. They didn't bother to tell us this until everyone else had deplaned and they wanted to know what we were waiting for. Of course, all of us missed our new connecting flight, which conveniently had been scheduled to leave concurrent with our arrival.
YMMV