We like Entry #8 but think it looks a bit like an alien. Could you try it without the eyes/nose symbol? Could you also try the head in a darker color so it stands out a bit more? Entry #7 looks good. The colors stand out and will look good on the vehicle and stationery. Could you drop the blue shadow so we can see how that looks? Entry #6 looks good too. The color variation has enabled the red in the headset which is true to the international standard. I don't think it needs the second headset on the o but it's a good concept.
Can you reverse the red and blue. As the international hearing standard is red cup to the right ear and blue to the left ear the blue muff on the right side is preferred. Either that or have a silver (neutral) color for the headset
We like #86 & #87 but colors would have to be reversed. The text in #87 looks like a MOBIL OIL logo but may look better reversed.
Your designs will look really good on stationery and our vehicles.