Between the one INFJ and the INTJ that I know, I definitely would fear the stare of the INTJ moreso than the F.
I think it more has to do with the way you get into the mood you do.
In my experience.. INTJ's have a very interesting way of balancing this "I don't care enough/it's not efficient enough to voice my irritation here." and "I don't mind saying what needs to be said/That's bugging me, so let's fix it by saying so."
My INFJ is misleading because he's very E for an I.. Insufficient data.
That being said.. I've been told that since I'm usually happy, or usually I tell people nicely off to the side the things that need to be said, that it can be scary to just give this angry stare. To see someone that's usually open and forth-right get angry in a way that's silent and piercing is unexpected and, thus, mayhap a bit more terrifying than from someone you'd expect it from.
If you're usually an outspoken angry person, or if you're not quick to anger, I'd say these two make for the most potentially fearful soul-piercing stares.