Sorry I travel 2 sometimes 3 times a month to Vegas and I have to say outside of NYC it's the biggest taxi racket out there. Because of the terminal locations, it's a guaranteed $10 sometimes $15 bucks before you even get to the Strip because of the circuitous routing and roads. One time I had a driver "miss" the airport exit and then had to argue with him over the extra $13 bucks on the meter because of his mistake. So now I rent cars when I go there and again, Vegas leads this category in stupidity. Hike to the Rental Car Shuttle Bus, ride for 10 minutes, more lines, more hassle and oh yeah nice "Franchise" fees on top of "Airport Taxes" to pile onto the car. Still, it's better than a taxi there.
If you go the non-highway route, it's pretty direct. There's not much "circuitous routing" at all. And compare the airport-to-where-most-people-go fares to other cities' fares - it's quite low. I'm not defending anyone trying to make your ride longer and charging for it, I'm just saying Las Vegas is one of the best cities in the country for cabs if everything's honest. Next time you get in a cab in non-peak times, say "Take Tropicana" if you're going to the South side of the strip, and say, "Take Swenson" if you're going anywhere north of City Center/Planet Hollywood. The cabbie will think you know where you're going and won't take you out of the way.
As far as renting a car goes, it takes an extremely long time unless you go to Hertz or Avis, who invariably charge double or more what the discount places charge. I made the mistake of renting from Dollar one time, and I certainly got what I pad for. At least a dozen people in line and one agent. On subsequent rentals, I see the same thing at Dollar/Fox/etc... - hideous lines and one or maybe two agents. I'd rather spend $15-20 each way on cab fare and save an hour, but if your time is worth nothing, then the discount places may be worth it to you.