TJ's seem to work. ISTJ, ESTJ and ENFJ are the only ones to get relationship status from me. I understand the ISTJ thing. It gets way too comfortable. I really like J's though. They bring a stability I need in relationships but also it's fun to try to shake theirs up. I enjoy that very much. Other P's we end up feeding off each other and it goes over the deep end...which is great for friendships but I want someone to pull me back from my own wildness sometimes.
However, that was a long time ago. As I get older, I see myself more interested in ENFP (I met one that blew me away. I thought I could really fall for someone like him if he was physically attractive

) and ESTJ (It's just so damn easy). I wouldn't rule out a fellow ISTP or ESTP but it's really difficult for the emotional dynamic to not end up with this sort of outcome:
[YOUTUBE="Un9Ek6IM_Kw"]xSTP + xSTP[/YOUTUBE]
I really think fellow xSTP relationships can only work if the Enneagram types differ in a compatible way.