I tested more than a dozen car phone mounts over the years and settled 2 years ago on the Kenu Air Vent, purchased through the Apple Store. It retailed for $35 - expensive but very solid and reliable. Unfortunately, I lost mine but found a similar looking one on eBay for 1/10th of the price (the grey one looks better than the green one pictured). It works exactly the same and feels as solid as the Kenu one! Perfect fit for both iPhone SE and iPhone 7 (any smartphone for that matter).
Delivery is from China and took less than 2 weeks to Sydney. Comes in nice packaging so makes a great gift as well.
Edit: There are apparently other cheaper sellers that still have stock (thanks Chickenleg), I can't vouch for their quality though (it's always a bit hit and miss with overseas sellers, especially with low priced items).
Edit (10/12): Price dropped from $3.79 to $3.59