300 is bordering on being non-perspective (like the side, top, and front cameras). However, it could be very useful for things like logo design. 25 MM increases the drama of the arrangement, but it also sort of creates the illusion the front figure is too far from the back figure to sock him one. 50mm creates a good impressiont that the two are getting ready to box and doesn't leave the viewer feeling that they are too far apart to get the job done. I'd go with something between 50mm and 25mm, to create tension and a real 'fight scene' if that's what you're going for. But you see how different focal length and depths of field lead to different impressions of what's going on. In 2, above, th character are boxing, and the back Mike is maybe takling to his agent behind the ropes. The music is something out of Rocky. In 3, above, the heightened drama from the lower focal length and increased perspective distortion creates a wholly different scenario. I get the impression that the back Mike has just been cornered in a dark alley where the front Mike is about to beat him up or stab or shoot him (you can't see his hands, and it becomes more important that you can't here). The music is something out of a thriller or Batman, perhaps. Much darker. The foreground figure becomes more imposing than the background because the heightened perspective makes him actually bigger on the flat screen, even though we don't think he's bigger, he seems bigger. Also note how the composition shifts between them. People naturally follow arrow-shapes. In the first one, the back Mike is taller, and the outthrust elbow of the front Mike leads the eye to follow the shape from left-to-right. That measn you 'read' the back Mike first. I the middle one, they are about balanced so you focus on both pretty much equally. In the last one, the smaller back Mike leads the eye right-to-left, so you see the front Mike first. This and the size change shifts who is the 'attacker'. The balance of the centre one giving the impression of a 'fair fight', thus the Boxing thing again. ALso note that despit ethe heightened drama of the third one, the composition is goofed up because the back Mike's face is suddenly shoved into the front one's shoulder. That woudl require some adjustment before using it, to avoid the partial-face-cutoff. So, really, it all depends on what will best tell your tale.