Friday at 7:30pm that weekend? You'll almost certainly wait more than 5 minutes for a taxi. As for a car service, the meet and greet is generally in baggage claim, and is a bit more efficient. You have to go a little farther to get to the car that you'll take to the hotel, but it's still convenient.

Bottom line? You're going to be miserable at the airport no matter what -- you're coming into Las Vegas on a Friday night, on a very busy weekend (135,000 people for the ConExpo wraps up on Friday night/Saturday morning, plus another 15,000 to 20,000 people arriving for conventions starting Saturday, plus the typical 50,000+ that come in for a spring weekend) and you already sound as if you're not happy about it. Hopefully once you get to the hotel you'll be able to unwind and relax a bit and enjoy your stay.