From reading news and reviews of all the systems out there, I tend to think the Ford SYNC system has the most versatility and road-tested stability. I've been a passenger in a few Ford cars with SYNC installed, and their drivers seem to have adapted to the unique ways you had to call to them: "Play FM 103.3," "Play Pandora station: Oh-AY-Sis," and so on. It's like reverse dog-training: you learn the commands, and your car rewards you.
But here's something I like, after some reading, about Chevrolet's MyLink: it's available on basically every car Chevy makes. There's no price delineation, or extra-super-turbo versions of it for the luxury vehicles: it's available in a roughly $14,000 Chevy Spark, and presumably every car up from there. And Chevy is out in front of Apple's Siri, announcing an intent to integrate Siri into upcoming MyLink updates.
Yet what I really want, and what at least one of my car-buying friends told me he wants, is a kind of fall-back option: just let me talk to my phone or tablet's built-in voice recognition through the car's audio/mic system. Phones will upgrade faster than car systems. New apps will suddenly become essential, a la Spotify's rapid gain on Pandora's streaming music crown. And it's much more viable for a car owner to decide they want a better phone, or faster data plan, than it is for them to hope that their car maker will keep up with the times.
Honestly, I'd rather they focus on brakes and airbags. Tell me that your car is very smart about passing along my voice to my phone, and I'll stop by the lot on an upcoming Saturday. Oh, one more thing—standard USB charger? Please?