Imo, I think Poppovich has ran away with it this year. There are a few candidates though. [poll coming soon.]
Popovich has it in the bag. He has managed the minutes of his aging trio very well, while at the same time developed the young talent. The real test will be playoffs though where age/injuries of Manu/Tony/Duncan will play a major factor.
I don't think it's super clear cut, though it IS between Pop and Thibs at this point. Thibs has his Bulls at the best record (unless Miami caught up) in the East, mostly without Derrick Rose this season. I'm not arguing that Pop doesn't deserve it; but Thibs deserves it more, IMO. However, Pop might win it just because Thibs won it last year, right?
I'm going with Thibs. It's incredible that Chicago has the best record so far despite of all the injuries they've had this year. If you look at that team it's not all that talented. Thibs gets the most out of them.
Between Thibs and Popp. Whoever finishes with the better record. Both teams have won under impressive conditions. Spurs being age and partly injuries. Bulls being injuries.