For the best results, I would tint the windows. To know what would be legal, I would need to know your location.
I'd say finding the best shop is more important than best tint. Go with a local installer that offers a brand name tint and a lifetime warranty against fading, bubbles, tint lifting, etc.
Yes Make sure your receipt is well printed so it won't fade over time My wife's film had an issue after many years. Hard to read the receipt but was accepted and fixed.
I just had an appointment made for putting in the 3M Crystalline, with the Air 80 on the top of the front windshield. The guy says that this is as good as it gets. $500 installed theoretically.
I did all the doors and hatch in 35% which is the darkest Missouri allows for the fronts. You can do limo dark for the rears in Missouri, I just didn't want the imbalanced look of two tints. Your credible installers can tell you your legal max or your LEO. My installer would install what ever I wanted if I wanted to roll the dice. And as has been said before find a reputable shop.