Other people’s criteria may differ though.(road)Sprinter friends of mine could snap Sqr taper axles, and I seen a few break on heavy landings.
Tom Boonen was using sqr taper cranks up until recently – can’t recall him snapping any – maybe your freinds should give quick step a call!
However i’ve seen sqr taper axles break on landings on mtb bikes (only un72 thou)
I think each style BB had it’s own advantages and disadvantages.
I quite discount the stiffnes thing for normal XC riding, as you are mostly spinning – and i dare say most decent track cyclists could put down at least 30% more power than most guys on this wesite and efficiency is paramount sucsess in track, and as flexability would reduce effeciency they would be the first to bin them.
Octalink – i always found them very good – it removed the problems of sqr taper (damaging cranks on landings) with very good durability – but slightly less than sqr taper due to smaller bearings.
ISIS – Filth.
External – good idea dogged by poor execution – especially by race face and FSA (my external road FSA BB disintegrated compleatly on a ride the other day) Shimano seem to have the best seals although i’ve yet to try hope etc.
My conclusion is that sqr taper offers good cheap long life option for those not doing anything to hucky. Octalink similar but can handle more abuse by the rider. And external good for heavy folk and those that jump off stuff – just don’t be a knob and jet wash your bike!