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I've already done all of Nathan Lowell's books. I started with him, as he is one of my professors currently. Been through him, Ballantine, and Gamblin. I'm about halfway through Sigler. I will say this, though. I do plan on buying Sigler in print. I'll add that to my personal collection.
I'll add the others to my list for whatever comes next. I found podiobooks to be a happy medium for me. I have a long commute to work (work full time), and I'm a doctoral candidate, so personal reading doesn't really happen for me right now. Lowell was really good. I wish he had slowed down a bit in the progression of the Solar Clipper series, personally, but otherwise it was great. Sigler's books are great standalone books. You don't necessarily have to follow the series of publication to keep up. I did follow the chronology with Barnes, but not Ancestor and the others.