The easiest way: reserve one.
The cheapest way: play around with different booking sites and codes you qualify for. Then book a non-prepaid rental and follow it with autoslash.com.
Color: I've seen most on the lot but red/black/silver/yellow ellow most common.
Type: good mix of the coupe, convertible and coupe GT. Knowing LAS, I wouldn't count on anything better than exactly what you book.