I found it very difficult to make any completely objective comparison of these four, Andrew. I prefer 1a without a doubt but I am hard put to explain exactly why in any sense which would help you. I have played through them five times using my old, but high quality Pioneer equipment, with good Mission speakers, forming an equilateral triangle with my listening chair, as I do with all my recordings. 1a is more intimate, with a slightly wider stereo angle, closer to the driver's seat, as it were, and a sound which strikes me as richer, but this reaction is probably just from listening so much to my own music recorded in my lounge. You get used to anything you hear often, and then you start to prefer it, then finally consider it superior when it probably isn't.
Of course the music is very attractive, and listening to it tends to override listening to the recordings - that doesn't help. I find it exceedingly difficult to listen either analytically or objectively at the best of times I'm afraid. Neil's comments are both acute and objective, and therefore likely of more value to you than mine; I have not examined the files themselves.
Anyway, the short, probably unhelpful answer is that I like 1a.
Topic: Comparative audio samples - opinions wanted