I like the simplicity of a key and the fact that there is no question where it is. My wife and I do this routine where we drive to the store together, I let her out, and she walks off with the fob in her purse.
One of our cars just lets it happen, the other starts chirping at us and she has to come back, dig the key out of her purse, coat, shoe, bonnet, or where ever its currently hidden and hand it to me, while we're blocking traffic.
When my cars are in the garage, I tend to leave the key or fob in them. With the fob vehicles, sometimes it was in my pocket, and it went into the house with me by accident, so next day, shit, no fob as I'm trying to leave for work.
I'm in the "solution to a problem that doesn't exist, or more like creates a new problem that never existed" camp.