i would just go with the HTC one. haven't heard anything bad about it.
the aftermarket ones probably work as well, but who knows if it is really 3500mah or not (damn thats huge)
i personally have an off brand 1750mah slim battery. it is the same as the stock one. not any better/worse. i have heard the same about the siedio one as well.
i charge mine up, and slip in in my pocket. once the stock one runs out (after about 12 hours) i put the new one in. phone is still thin, and light enough to not bother me and the swap takes 2 minutes.