Zion National Park

Anyone go up Hwy 89?

I too came up from Las Vegas using I-15 to Utah 9, which goes all the way to Springdale at the entrance to the park. I stayed at the Zion River Resort in Virgin, UT, which is very nice.
Note that I-15 goes through the Virgin River Canyon in Arizona, which has ascents and descents that are steeper than you may be used to on most interstates. They are necessary since the highway passes through some very rugged, though scenic country. Apparently it is known as one of the top engineering feats of the US Interstate system.

When I did it a few years ago from Vegas. I took Interstate 15. Great route.

What would you consider to be a best route? Interstate the whole way? Side roads?

I use Google Maps to show me the way and it's been very beneficial. I also use the Motor Carrier's Atlas to see if the route is approved for truckers.