I tint the windows on all my cars, I prefer a metallic hybrid tint around 40-43%, 50% on the rear window. 40 is darker than 50% but lighter than the standard 35%. The lower the %, the darker it is. I prefer it lighter on the rear window. You can't tell the difference just looking at the car but it does make night driving easier.
You can find lots of tips online but the basic types are dyed (gets knocked by tint snobs but any quality dyed tint is fine), metallic (has metal particles in the dye to reflect heat without making it darker), and ceramic (has ceramic particles to reflect heat without making it darker). And then there are the semi-hybrids which are a mix.
I like semi-metallic since it has a lot of the benefits but without the shinier look of a full metallic. dyed and ceramic aren't as shiny. This is just my subjective feeling, but I feel a difference in how hot the light feels with metallic vs. dyed at the same darkness level. Ceramic is very expensive and hard to find. Metallic is only slightly more expensive than dyed. Metallic will kill your AM reception, dyed and ceramic won't. My cars w/metallic hybrid tint doesn't have any problems with ez-pass, FM, sirius, GPS, or cell phone reception but I think the AM got a little worse. i don't listen to AM so I don't care. Make sure to only use water and a microfiber towel to clean the tint. Cleaners like ammonia based products and dirty cleaning tools can scratch the tint.