ziggy75,
It depends
But you knew that...
First, what transmission do you have or plan to use?
I use C-6 automatics which have a 1:1 ratio in third. I use 2.73 8.8 rears and am very happy with the results.
If you have or intend to use an overdrive trans, you may want a higher number axle, say 3.55 or 3.73
To find out what ratio is installed in the rear you have, count the ring gear teeth (the large one with the big hole in the middle) and the pinion gear teeth (much smaller with no hole). Then divide the ring gear count by the pinion count. An example is: ring gear 41, pinion 15, so 41/15 = 2.73333 which is called a 2.73
Hope this helps,
Tom