Oh lord, @Zarathustra, you've opened the flood gates of ENFPdom.
I. Relevance to Thread:
To be honest, as much as my little theoretical mind recoils at the thought that reality might actually have a grip on me for once, I don't think it's entirely useful to say what type is better for who. I believe there is something about love that really messes with quantification.
I believe that ENFPs can be great for INTJs and it sounds like INFPs can too. I suspect that ENFP-INTJ relationships have an easier time dealing with the practical world and I suspect that INFP-INTJ relationships have an easier time balancing alone time with together time. As for who's better for who - I don't think it can be done. I don't believe it should be done. There are so many confounding factors - age, upbringing, childhood, previous relationships, beliefs, values, goals, desires, needs, gifts, weaknesses, health, culture, education - and they can't be isolated; they're all synergistic. All combine to make people what they are. Type can play a major role, but I don't think it's far-reaching enough to predict all relationships.
In this thread, in this situation, INTJ guy clearly feels something deep for the INFP. I agree with @mia that both types should be equally considered, and I think @Coriolis' advice here is spot-on.
II. As for Everything @Mia.'s Said:
Well, honestly, most of it is pretty offensive and a glaring misinterpretation. ENFPs are a different breed and our objective value in relationships can't be judged solely on an INFP's set of standards.
1. We flirt because it makes people feel good about themselves and it makes people smile. I have learned that this can mislead people and I try not to engage people in any way that they would think that I have anything beyond platonic intention. I think this is a surprising lesson for ENFPs because others' "flirting" is our natural behavior. The truth is that when I like someone, I tend to clam up and get distant; I become quiet and hypervigilant. Flirting just to say "you are special to me" is easy. Communicating "you are more special to me than everyone else" - that's a lot more of a challenge and requires learning about the other person before acting.
2. Introverts and extraverts keep their selves in different places. We can both be equally deep, equally intentioned, equally committed. But extraverts are constantly engaged by the external world, and you have to allow for that in relationships. It's not about flightiness, or about whatever you call "volume" - I actually have no idea what you mean by that, but it surely doesn't sound flattering. With two introverts, maybe you'll be content to sit there and gaze at each others' navels for eternity, so to speak. Extraverts are going to need external stimulation. It doesn't make us superficial - truth is, in some ways we have a better concept of reality than you.
Moreover, it's not really an apt comparison to say "twice the volume" with ENTJ:INTJ::ENFP:INFP because you're talking about Te dom : Ni dom :: Ne dom : Fi dom. ENFP isn't outputting twice as much; we're actually taking in twice as much. INFPs have twice the internal structure. If that's what you consider "twice the depth", okay. I find my depth more in my concepts and ability to communicate than in my feelings. I imagine an ENTJ would say something similar about finding more of their important self in their actions and accomplishments.
3. It seems like people falsely assume that for ENFPs enthusiasm and excitement equals commitment or dedication. In my world, these two things do not equate, and it's hard for me to understand why others equate them. As with flirting, I have learned this difference through experience and observation, and have worked to tone this down as I've grown up because I don't desire to mislead others. But! to a certain extent I don't feel like that misinterpretation is entirely my fault, nor do I feel like I should have to restrain my happiness because others don't understand it. Learning that everyone doesn't operate like you is a huge part of growth in a relationship.
4. ENFPs are humans too, not flitty butterflies, and our love can deepen and grow as well. However, unlike with many INFPs, we don't care to openly share our darker, sadder, more anxious side with the world, and certainly we're not going to shove that in the face of someone we've just begun courting. That's a discussion to be had later when the relationship has stabilized - and the more I love someone, and the more I trust them, the more I let them in. So I feel like with ENFPs it probably is easier in the beginning (we LIKE the game!), and then there's a harder part after the initial stage where we start opening our darker, deeper selves up. And it is really easy at this point to get scared and run away. Because, as INFPs should well know, people don't always want to accept that darker side of you. They think you're crazy or unstable or far too emotional, or all of those things. So yes, the relationship with an ENFP is going to be more challenging later - but not increasingly challenging into forever. Just instead of a huge bump at the beginning like with INFPs, there's probably going to be a small bump at the beginning and then a bigger bump later.
6. We do have grass-is-greener syndrome - but quite frankly, I suspect a lot of INFPs do too (it's not like you guys don't have strong Ne) - it's just that INFPs wouldn't sacrifice the Fi stuff for the Ne stuff, whereas we might. At the same time, that "flightiness" - need for novelty - can be satisfied without sacrificing commitment in a relationship. We can redirect that energy into being planners, travellers, good hostesses, designers, creators, innovators, voracious readers - just because some ENFPs run from commitment doesn't mean the group as a whole is doomed. If anything, it can make us stronger in terms of supporting the synergistic couple, since we are almost always ready and willing to interact with the world, partner included, and we will be constantly bringing new information into the relationship with the goal of bettering it.
As for myself - one day I asked my ESJ if he ever thought about being with other girls, because honestly I was seriously thinking about how it'd be to be with other guys. You know what he responded? Sure, I think about that sometimes. WHAT A RELIEF. And so I laughed. And we talked about our thoughts, and mutually agreed that we rather enjoyed our relationship. And then we snuggled and went to sleep.