It depends which rim you’ll visit.   Las Vegas to Grand Canyon North Rim is 265 miles and takes about 4.5 hours.  The distance from Las Vegas Airport to Grand Canyon Village on the South Rim is 280 miles and, although it is further, it's on better roads, so takes about the same amount of time.  From Phoenix Airport to Grand Canyon (North Rim) is 355 miles and takes almost six hours.   Phoenix Airport to Grand Canyon South Rim is 235 miles | 3.5 hours. So, it’s better to fly into Las Vegas for Grand Canyon’s North Rim and better to fly into Phoenix for Grand Canyon’s South Rim.   This doesn't take other factors into account, though.  You might like to start or end in Las Vegas, or you might like to stopover in Sedona on the way to/ from Phoenix.  Although many people choose to fly to/ from Las Vegas, in fact it’s quicker to get from Phoenix to Grand Canyon National Park than it is from Las Vegas. At least to the South Rim.