The reason why I prefer #16 to your other designs is that I feel like when there is too much emphasis on the initials HD -- we think "High Definition"... that is why the letters need to be approached more creatively/artistically, etc... #18 is also in the right direction. I like the color scheme, would like to somehow see it appear more high tech and finance related through icon/metaphor. I like the "A" in digital in #17 and #18... also #12, #13, #14 are example of to linear "HD". I hope this helps, excellent work.