For me the first two are the weakest. The first, as you point out, has a cluttered background and that has limited your options. If you were to move the bike to a better location you could try out some more interesting angles. In the second one your subject (the exhaust pipes?) are too far over to the right - too close to the frame edge and the stuff on the left is not out of focus enough so it is quite distracting; especially the yellow pipe.
Three focuses better on a single subject though I would probably have cropped off at least some of the bottom of the image or shot from a different angle. That large blue piece is distracting.
Number 4 is getting there. A clear subject uncluttered but the image just lacks a little punch. It is a little documentary in nature and not creative enough for me. Maybe a slightly lower angle/narrower DoF to throw some of the text slightly out of focus, or else a more grungy post processing approach.
Number 5 - kerching (sound of coins pouring out of the slot). We have a winner. This is my favourite. I like the lighting (blue is quite moody), the subject is clear, and thanks to the lighting it is one of the brighter parts of the image (hence it attracts the eye) plus most of the distractions are well out of focus and dark, which makes them a lot less distracting. Personally I would have gone in with a local adjustment brush in Lightroom and darkened down the background/floor just a fraction to ensure the subject was the brightest part of the image (but only by a fraction). very nice shot.
