Answer: Brugia malayi
Thanks to everyone who wrote in - you all got this one right. Shown are clearly sheathed microfilariae with a clear space between the terminal and subterminal tail nuclei (arrows below). The deep pink color of the sheath is strongly supportive of B. malayi, although sometimes the sheath can be clear.
A couple of my former students recalled my favorite ways for differentiating the sheathed microfilariae (thank you Trish and Neal). The 3 sheathed microfilariae can be remembered by the phrase Wears Long Britches (W-Wuchereria, L-Loa loa, and B-Brugia). I think of the sheath as a long pant leg (britches or breeches for my English friends).
When a sheath is identified, then the 3 genera can be differentiated by the characteristics of their tail nuclei. The tail of Wuchereria bancrofti is Without nuclei, the tail of Brugia is Bi-nucleated (or makes a ba-dump-a-dump pattern, a phrase courtesy of Heather), and finally, the nuclei of Loa loa "flowa flowa" to the tip of the tail.
Everyone has their own preferred way of learning things, so if these silly tips and tricks don't help you, feel free to disregard!