It's a tie for me:
GI Tom's BATs vs Joes in Delta Accelerator suits - I like the sense of movement and apparent chaos as these troops clash. I'm rooting for the BATs!
Prince Adam's Night Vipers (take 2) - I like the composition and depth, along with use of the G36 rifle. It's about time v1 gets a weapons upgrade. If only the lighting was a bit darker...Anyway, these troops look sinister as they march across the landscape.
Scarviper's Red Alley Vipers - Nice lighting and depth. The figures' red color is highlighted and works in the AV's favor. I myself have several of the blue-and-gray version, but this photo makes me want to hunt for the red ones!