Never used any of those but I use ProClip mounts, they are pricey but really nice. They have one with a built in dock connector, so the iPhone just slides in and connects right up, no fumbling with cables every time you get in / out of the car.
You can also buy a cable which has a dock connector on one end and a USB (for power) and line out (for AUX hookup) on the other end. I do agree the FM transmitter things suck - I've own two and both were terrible, finally just swapped out the radio for an aftermarket deck with USB input and was much happier. Got lucky with our newest car as it has an AUX plug already in the armrest, so I didn't need to do anything but add the ProClip + audio cable + micro USB 12V plug so it charges the phone.
I would see if there is a forum for your particular car and see what other owners recommend as a good factory interface. Each make/model is different so you'll get better ideas for people who already have the same car.
My equipment list is
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. Playstation Network ID = jmii ...that's JM roman numeral 2