Well, both ENFJs and INFJs love to help people, and a friendship is more than suitable for the two- but I really can't see myself in a relationship with one.
I have a lady ENFJ friend, and we have a really nice brother/sister friendship. The relationship thing wouldn't work because we both are 'workers' that will go out of our way to help each other, so we'll constantly butt heads. I'll go to clean something in her car, and she'll say, "No, I've got it," and I'll say, "No, it's all good- I've got it." It's a bit of a power struggle. Also, we both talk in hidden meanings, and there isn't enough of an Ne/Ni relationship to pick up the other meaning in what we're saying, making communication a little awkward. This also attributes to a lot of confusing, indirect contact, making me (and her? I'm not sure, which only proves my point) a little suspicious of what she's really trying to say.