Like always the "stock" Dana is stronger than a "stock" 9" Now build a 9" without ANY Ford parts then the race is on. Three bearings to support the pinion against the ring gear will ALWAYS be better than two  And yes it will cost about twice as much but in the end you will have a better unit. Still have a Dana in my car though  Gus  100% agree  Build one w/ good parts and the 9" is better. That efficiency argument is a wash. You'll never see it, unless you're in a low powered class car that needs every tiny ounce of free movement to run a number. The benefits of an aftermarket 9" far outweigh any efficiency issue.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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