I'll qualify 'better', by saying we're talking here about durability in the touring context. If you have had problems with bottom brackets snapping after getting 'big air' on your jump bike, then you are probably outside our frame of reference!
However it was these 'snapping' issues that prompted Shimano to look for a new design. By increasing the diameter of the BB axle, they radically increased both it's strength and stiffness. There were also weight advantages when you hollow out the axle as material here contributes very little to these properties. But now they had this bigger diameter hollow axle, they had to find a new way of attaching it to the cranks as the old tapered square spigot didn't scale up well. Hence the 'Octalink' arrangement.
However, as a consequence of enlarging the diameter of the axle, but not enlarging the bottom bracket shell on new bikes (as they did with the head tube when moving to a larger headset size, and would have had loads of advantages in itself), there was now a reduced space for the ball bearing races. Despite trying multiple rows of little ball races and even roller bearings, nothing proved to be anywhere near as durable as the old chunky bearings in the previous generation square taper versions. ISIS (the patent avoiding clone of Octalink) was even worse in this regard, with some high end BBs only lasting one two hour ride before play appeared. Also the construction is such that when worn, the ball bearings can escape and the unit fails completely, rather that carry on, albeit rather roughly. SKS (?) have now introduced a version of the ISIS which is reasonably durable, but is something like £80 a throw.
The solution for Shimano was to redesign the whole thing with the bearings on the outside the ends of the BB shell, where they had the space to return them to the original size.
To disguise what was essentially an engineering cock-up, the marketing guys at Shimano spun the cover story that all these changes were done in pursuit of the 'stiffness' pros demanded for sprinting. However this flew in the face of reality: the dominant sprinters at the time were Boonen and McKewan who seemed more than satisfied with their Campag square tapers!
Despite the new external bottom brackets being produced (in a long winded, round about way) in response to the problems experienced by extreme mtbers, there doesn't appear to be anything wrong with them now for touring either. But then there wasn't (isn't) anything wrong with square taper either! Therefore my advice to anyone looking around at old mountain bikes for touring is to avoid one of the cock ups (Octalink / ISIS).
