I'm looking upgrade my rear axle whil I'm doin my 4wd conversion wats a good replacement to the d30 I have and wat can I pull a better one out of? I have a 2000 Cherokee sport

 

most here will say the ford 8.8 with disc brakes and 4.10's out of an exploder.
then you just have to find a d30 out of a 4cyl 5spd cherokee to match the 4.10's.

but if you can find an xj44 from an 87 cherokee, i would go with that as it's a bolt in axle. just be sure to grab the drive shaft with the 44.
most of these are 3.55, so practically any xj d30 has those gears and is an easier find, but those 44's are getting harder and harder to find these days.

otherwise, if your xj now has an 8.25, i wouldn't worry about changing that. just find a d30 from a 97-99 cherokee so you have the proper hubs and brakes with the hp30. don't get one from a 2000 or 2001 as they're low pinion.

91-96 d30 might all work the same too.