Be sure to compare the girth measurements of each bag to your own (measure your shoulder girth over your arms and while wearing all your insulating clothing). The Hummingbird is an inch narrower in shoulder girth than the Ultralite, which is too narrow for many people. At the hip, the reverse is true.

Both are high quality sleeping bags, with little, if any, difference in quality. To me, the draft collar (the "neck thing") in the WM Ultralite often makes the difference between being comfy and being cold. I can leave the hood relatively loose for ventilation (or at least for avoiding breathing into the sleeping bag) yet not have any icy drafts down the back of my neck. Others may differ.

On the other hand, you can get far more custom variations in a Feathered Friends bag (for a price, of course).

I came really close to getting a FF bag, but decided on WM instead. That's mostly because at that time (or at least from Backcountrygear.com), the WM was slightly less expensive. IMHO, you won't go wrong with either.

BTW, in my old age, I've finally learned my lesson about basing buying decisions on weight (or price) alone!