You didn't mention your specialty - when I went to Vegas in 1996, I was in the ED and I LOATHED it at Valley Hospital, quit within 3 months. I also worked at UMC and loved it, I later went into the OR at UMC and also liked it and was there until I left the States to come to Germany.
UMC is the county hospital and the only Level 1 trauma center for 4 states, so yes it is busy, but if you're a newer nurse and looking for experience, you won't beat UMC. For personal reasons I choose county facilities over private ones and that may be another reason I'm partial to UMC, but you still can't beat the level of experience you would get at UMC. Though be aware that at UMC the ED is divided (actually into separate bldgs connected with a corridor) from the Trauma Resus. area and are 2 separate depts, with a 3 suite trauma OR and Trauma ICU beds on it's side. Peds ICU is also in the trauma bldg but upstairs.
Financially, the pay is fairly equal with other area hospitals as are benefits and you do not pay into social security at UMC (so unless you've been working for enough of your life to be eligible for your 26 quarters (or however many is required) to become eligible for SS, you may not want to go the UMC route unless you plan to stay the whole 20+ years with them. It's nice to have that little extra from not paying SS tax, but down the line you may regret it. You DO pay medicare taxes.
Sunrise (main) was finally designated a Level II a couple of years ago and has the Children's Hospital in Vegas (if you're a Peds nurse), but unless you live REALLY nearby, it's a pain in the butt to commute to, it's kind of 'locked in' away from the intetrstates by some of the busiest, most annoying surface streets (Sahara and Maryland pkwy - ugh!) I've ever had the misfortune to drive. You'll be tearing your hair out if you hate commuting like I do. There is also Sunrise MT. View which is right off one of the interstates in the NW part of Vegas and not as annoying to get to, but no Trauma designation.
Vegas is an odd place. I can't say I miss it, except for the fact my children live there - otherwise I'd never step foot in the state again willingly. It is a right-to-work state (you can be let go at will), so nurses are very much at the mercy of the hospitals, though contracts were looking better when I left, call pay had gone to $5/hr and the salaries generally tended to be higher than other surrounding states (other than CA).
I personally hated the heat, the awful traffic, the whole gambling/strip club/bar pervasion of the place - do you REALLY need slot machines at the gas station and 7-11 and the supermarket?. If you have kids, there really is nothing left for them there, when I left they had torn down the Wet'n'Wild and had just shut down the Scandia fun center (pending demolition) and the zoo? I'd hardly all a llama and a donkey a zoo. But that's me and a lot of people love it there. Don't know if any of this helps,
Best of luck to you