Wow, that's a toughie! I'm just gonna go with the one I most often fantasize about, and that would be the second. It would be heavenly to have someone really see and accept me.
Sure, I have been wishing for the autonomy of the first one, but more in a "What If I didn't need other people like I do, I wouldn't have to feel insecure, ever!"-kind of way.
I find them equally realistic, and here is why:
When I say someone that understands me. I'm talking of someone that sees the whole of me, that understands me just as well as I understand myself. Something that I deem impossible, as there is always going to be a part of you that do not transcend into the external world, people are simply not able to connect on that kind of level. It's also important for me that the communication goes both ways, with me being able to understand my partner just as well.