Trying to choose a favorite IMM is like trying to choose between a list of diamonds at 100+ carats. Sure, each one might be differently cut to suit the needs and wants of certain groups, but in the end, I wouldn't want to try and justify the idea that one is particularly more valuable than any other.
Despite the fact that I'm pretty sure that they use lasers to cut them now, it was an old belief that only a diamond could cut another diamond, which fits perfectly with my analogy in that the IMMs we have now are products of each other, past IMMs, and the players around them. So, passing judgment on them is like passing judgment on the old IMMs, both good and bad.
I suppose I'm closest with Algorab, Thuban, and Achernar. But I can very much see the hard work and drastic changes to this game made by Wert and Sadr. Jinn's Algorab deserves some specific mention, as well. I was really sad when she had to leave, and I chose her as my favorite a LONG time ago. I've only seen a little of Sargas and this new IMM, but I've yet to have any complaints at all, and what I have seen has been great. Dulrik, Sadr, and Alshain should get props simply for the hours they've put in and how long they've done it. Though, Dulrik always has the place at the top, being not only the implementer, but the very reliable father of this game.
I don't agree with every change that has happened in this game, but I'd have to say the Pantheon as a whole is my favorite, include those who were good, bad, or otherwise, simply due to the fact that they keep the game moving forward. So, props to you all.