Volt, I had a handful of unbranded NP-550 size L batteries from some LED lights gathering dust so I got one of SD's L sleds. With one in each of the sled's sockets it's just a bit thicker than the recorder itself (and roughly the same thickness as the Hawk Woods single L sled). I get plenty of record time out of two batteries for my needs and can easily hot swap in a spare. I prefer the all in one form factor that the L batteries provide and two of the batteries are lighter than my USB battery pack. If an extremely long recording situation comes up I can use my Anker 20100+ (again, already on hand from another task).
If I hadn't had either on hand to begin with I'd lean towards USB powering. On a longer trip I have coming up later in the year, I will likely bring the Anker since I'll be carrying it and its charger anyway (and the one charger also charges my phone and camera batteries). The L batteries mean one more (large-ish) charger to pack.