I don't have any experience with Avalon mining gears but I trust the other gentlemen's judgment, so reliability wise, I think Avalon beats bitmain easily, if I had to choose one gear in the world it would be Whatsminer M21s, but since that isn't in your list I would go with the S9.

While an Avalon gear could be more robust than S9, the latter is a lot more popular and has a variety of custom firmware that supports it, so you can get anywhere from about 10th at 800w range to a lot more powerful gear of 15.5-16th, also the spare parts are available everywhere, of course, you want to avoid the (K) and the (SE) versions as those are far from reliable.

With that being said, the Avalon 841 and the Bitmain S9 are pretty similar in terms of efficiency, so between the two, it would be a matter of cost per terahash.