In the UK 'limo' tint is the darkest and imo it looks too dark - it's only for barry boys. 'Smoke' looks quite nice, but it would be illegal on the driver & front passenger windows in the UK. 'Light Smoke' is quite nice and although it may well also be illegal on the fronts, you might just get away with it. I've toyed with the idea of light smoke on the fronts and Smoke on the rest (except the windscreen of course!).
Whatever you do, check the legal position first, so you know if you're breaking the law in your part of the world - and bear in mind that car glass is often already tinted to some extent. For example, the glass on my friend's car was already factory tinted to the UK legal limit before he put the tints on
UK legal position is maximum 30% tints on the front side glass and no restrictions on glass behind the 'B' pillar. Don't tint the windscreen at all!Also, go for Titanium film - it's better quality.