I always use ProClip. There are those that think they're expensive but you do get what you pay for IMO.
They have a IP mounts with pass through dock connectors. They could certainly be used for what you're looking for but you'd need to provide the solution that takes line audio from the dock connector and provides power to the dock connector. I used iSimple's IS75 for that. You'd also need a vehicle mount as the ProClip mount is just a device mount. ProClip does make vehicle mounts but I strongly recommend looking at Panavise or other manufacturers that make more solid vehicle mounts. ProClip tends to rely on friction and double-sided tape where Panavise's mounts actually bolt down securely to the dash.
"Ultimate" is highly subjective. There's no way that any solution relying on FM modulation would be ultimate to me. YMMV, of course. Audio quality always suffers with FM modulators. You can't beat hard wiring for audio quality.
Originally Posted by accessoriesguy
If audio quality isn't a concern, FM modulators are convenient as there's really almost no installation effort required.