Stick to anything Korean or Japanese and you'll be fine basically, they are in general the simplest to tint for virtually every reason. Most 'American' vehicles are fine too (except what's been mentioned for certain issues). Avoid German's and high end vehicles. And this is being said if you have guidance, training and can self correct issues with your own work.
In a perfect, magical, unicorn filled world, I'd only tint new trucks and cheap foreign hatchbacks and as many as I wanted every single day. In that magical world, with a never ending stream of those, I'd be rich, happy, never ache and do whatever the $#%@ I wanted with my spare time
Have a good system/order of things in place when you install and always follow it. Extra steps taken and trips around the vehicle add up on the clock, doing things out of order leads to slower working and more chances for mistakes/contamination/etc.