IMO, one point in imp fire nova totem is a waste. It's one of those all or nothing things. If you're dropping these for stuns, you want to be sure to stun.

If I had to choose, I'd probably go with imp fire nova. I have this on all 4, and with round-robin, it's around 8 sec of stuns on EVERYTHING. This can be a big saver of a bad situation.