Imagine a pond. ENFPs with Ne are generally like a pebble skipping across the surface, with frequent but shallow insights. INFJs with Ni dive into the pond, and generally have less frequent but much deeper insights. Deeper insights will leave a bigger impression, making INFJs seem more insightful, but I think they are equal, in their own way.
I'm actually surprised I've never noticed this topic come up.
In terms of "being psychic" about people- ENFPs and INFJs are the best two types (for obvious reasons). I've been fascinated by INFJs ever since my first girlfriend was one as a teen, and we had a "next level" intuitive connection. We could both kind of sense each others' intuitive abilities, and it often felt like we were communicating at a subtle intuitive level that no-one else would even notice, let alone understand. We also both predicted two of our mutual friends getting together from the first 5 seconds of watching them meet (literally a bit of eye contact and ordinary conversation).
Who's more insightful?.. I honestly think it depends on the individual. Whenever I meet INFJs (which is rarely- you guys really are rare) I always seem to get that "eye contact communication" thing going on with them, in a way I never even get with other ENFPs. However, our intuitive insights seem to match pretty evenly as far as I can tell (of course INFJs always seem to have an extra layer of mysteriousness so who knows what goes on in there).. but at least in terms of my gf when we were very young- she definitely beat me out. At that age I always felt I understood people better than anyone I would meet my age, but she was probably the only person who I sensed out-matched me. She is also the only person who successfully pursued me (by making me think I was the pursuer.. lol).
INFJs are incredible. I guess we can be pretty incredible too, but I take ENFPness so much for granted because I'm so familiar with it.
It really depends. Personally, I've found myself to be waaay more insightful than some INFJs I've known in my lifetime, but at the same time I've met quite a bit of ENFPs who....*ahem*....have no idea what they're talking about due to a lack of maturity, which I believe to be a key factor in all of this. Due to the fact that ENFPs have a tendency to be delayed in their process of maturing, they honestly have less insight. I have had the opportunity to meet multiple INFJs that have been absolutely clueless, and in their immaturity and judgement have entirely misunderstood me and misjudged me. That's not a surprise though, because the severity of my uniqueness kind of comes with the curse of being misunderstood and misjudged by most people in the short term, but sincerely loved in the long term. In short, it takes a looooong time to get me. I'm active in helping others understand me, BUT it still takes awhile because everything in my life is a long story, no joke.
In summary: My point is that it depends on the person's maturity/life experience. I personally find myself more insightful that any other INFJs I've met, BUT out of the INFJs and ENFPs I know, I can rely on the INFJs in my life for more insight than the ENFPs I know before they are more mature.