I have not heard the others, but you cannot go wrong with the JL 113, espcially for music. They are not the deepest of subs, but they can keep up with the mains in terms of speed and truly dissappear.
I would take two F112s over a single F113. More even bass response in room, possibility of stereo placement. Also rumor has it that JL employees prefer two F112s as well.
"the following subwoofers and which would you choose and why"
Of your choices, I would select the B&W 855. I know from personal experience how well the ASW 850 integrates with my system. This sub can go really deep and is easy to setup. I have heard many recommendations for the F112 or F113, but have nor heard them.
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