Depends what you have planned for it.

I did a whole cost analysis for the 8.25 and the 8.8 for what I wanted; gears, lockers, etc.

8.8 was more expensive by like $100, but was stronger, so I went with that. Could have done the 8.8 for $450 if then backing plates weren't toast, and I kept some parts from my 8.25.

I only ever plan to do 35's, but for the $100 more I figured it'd be worth it.

 

i went with the 8.8 because of the aftermarket support and also i got my 8.8 complete with 31 spline, disk brakes , limited slip and 4.10 gears at pull a part for 75.00. after mounts and new u bolts ,truss, diff cover and driveshaft adapter i still had less than 400 in the whole set up

 

I have the ax-15 five speed

 

I did the swap D35 to an 8.25/29 spline, & running 35" MTR's. I also swapped a HP D30 in the front (both with air lockers & w/stock axles). regearing is a must, 4.56 gears are great for 33's, but if i had to do it again, i'd go with 4.88's.... With our XJ's loaded down with gear &/or pulling a trailer 4.88's are a must, part of trail riding, is getting to the trails & back..

 

i landed on a 29 spline 8.25, BUT, i dont have any money in the axles really. i bought a parts jeep with the 8.25/d30 with 4.10s, wonton steering, and a detroit out back. i got those and lots of other goodies off it and made money off of the whole ordeal.

so really i only have like 250 in my axles (diff covers and rear disks)