The 742 is generaly regarded as the best. The 741 has a 1&3/8" pinion as opposed to the 742"s 1&3/4" pinion. The 489 has a 1&7/8" tapered pinion, which is actually larger than the 742's, but it uses a crush sleeve instead of shims to set the pinion bearing preload. This is less desirable on a high horsepower application due to the fact that the crush sleeve can collapse more, allowing the bearing preload to change. Most rear end companies now have a kit that uses a solid sleeve to replace the crush sleeve in the 489 and shims to set the bearing preload just like you would with a 742.
For most street applications any one of the three carriers will work fine if set up properly.
