Force of Nature - Immerseus, Sha of Pride, Iron Juggernaut, Malkorok, Thok.
Incarnation - Fallen Protectors, Norushen, Galakras, Dark Shamans, General Nazgrim, Spoils of Pandaria.
Please note I have taken DoC 100% of the time so far on these bosses.
Rule of thumb seems to be - Incarnation mutli-target, FoN single target
DoC only beats HotW on definite multitarget fights though
In my experience DoC has beaten HotW by a large amount every time I have tested my DPS. All of these tests have been self-buffed against a single raiding dummy though. Obviously, however, with it being a single target test I have to question if HotW does come out ahead. It may be something that depends on gear, and I'll test it out again at some point to see if anything has changed. Last time DoC was ahead of HotW by 5-10k no matter what tier 4 I used though.
I think you should choose what you prefer.
Personally though I pick Incarnation and stack it with Nature's Vigil for high burst because I like to stack CD's. Nature's Vigil also helps out with healing a little bit during healing demanding situations.
Depends on gear really but personally my best bursts always come from FoN+HotW. The treants hit like crazy with pot and trinkets+synapse springs. Imo only reason to pick NV ever is for the healing effect it gives but only when there isn't some specific part on that fight where you could have your Hotw Tranq up.
Only boss so far in this tier where i've used NV was Sha of pride heroic which we 1 healed and i wanted to have more healing going on in more constant way rather than one big heal.