1st Marathon. Vegas, Sacremento, Phoenix, Carlsbad?

My vote would be Phoenix.

It is a very flat and fast race with usually good weather with excellent on course support. (Spectators and plenty of water and nutrition so you won't have to carry anything)

Carlsbad is a great course but has some pesky hills that can be tough to manage if your not careful. (But of course the scenery is spectacular) I live on the course and regularly train the hillier parts of the route.

Sacramento is a good race but it is a net downhill with some early hill work that has proven the undoing of many marathoners. Unless your a really good downhill runner, you might want to file this one away for your BQ attempt. If this sounds like a good time, you might also consider Tucson. (Similar course profile)

Las Vegas is not bad but with a 6:00AM start, there won't be much on course support. It has also been getting mixed reviews from runners (organization issues) who have done it in the past. It is also a bitbumpy but if hills are your cup of tea, rock on

Phoenix is a good destination race mostly because hotels are cheap and the desert can be a pretty place. (But you won't see much if any of it from the course)

Carslbad is an excellent destination for a race and the scenery from the course is awesome. (Lots of unobstructed ocean views along the way)

Did Vegas in 06 and the course is only interesting from running down the strip, maybe first six miles.  After that, notsomuch.  Volunteer shortages had them condense water stops.  Didnt hear much improvement in 07.  Might go back someday, but wouldnt suggest it for a first unless you want to see Vegas.

I have not done any of the races you asked about, but I am signed up for CIM this year.  I picked it because of the its small size, location and net downhill.  I'm looking for a PR and hope this will be the place to get it.  Why not try it?

For my first marathon, I chose big (Chicago) for the atmosphere and crowd support.  I would think Phoenix would be that local, especially with all of the music. 

X2, only I did it in '05. Major complaint was that they couldn't even get the mile markers right.

If by Phoenix you mean R'n'R Arizona, it was better organized than Vegas but not a whole lot more scenic, nor a whole lot more crowd support.

I haven't done either of the other two, but I hear nothing but good stuff about CIM.

Go to:  www.marathonguide.com and read all the reviews abotu the races you're considering- that should help you make your decision.  I haven't run Vegas yet, but after reading reviews year after year andseeing very little postive comments about the race, I've bumped it to the bottom of my list.  The reviews are really helpful IMO.

x3 did Vegas in 2006 (half-mary) and will probably not go back. poorly organized, no scenery after the strip but loading docks

It's an excuse to go to Vegas though.