As others have mentioned, "Best" is very subjective regardless of what it is. The HE-400i is a good value for the price and is, what I believe, a direct result of many of the contributions made through various comments, modifications and tweaks that were performed by many to the Hifiman headphones on this site. It appears to me that Hifiman was carefully reading the posts and listening to what customers who owned their current products were saying. Many of the gripes that I had, were resolved with the HE-400i. To be honest, I didn't think the 400i would undergo so many changes. As others say, the HE-400i is different beast than the HE-400. I'm a bit surprised that Hifiman didn't label it the HE-460i. It would seem more fitting - in my view.
I can agree with you. I also happened to own the T90s for a short period of time. I found a new pair right in the price range of where you purchased yours. To me, it didn't offer enough of a jump over the Beyerdynamic DT-770. Or rather, that was just how I perceived it. Granted, they did use the Tesla technology with the T90 model.
For nuts like me, to narrow down a top-5 on headphones would mean that the "5" would most likely transition on and off that list based on past purchase history. But, that's just me and I'm trying to mend my addiction spending habits.