90s and earlier are the Renix era motors. Closed cooling system (although pretty easily converted to open cooling system). Lots of people love em, while lots of people avoid em.

91s and over are the high output motors. Open cooling system.

00-01 have the 0331 head which very commonly cracks.

Over the years the axles, interior and exterior features, etc. varied. It's really all preference though.

I love my 96. The year right before they changed up the whole exterior look (I personally like the older look). I have gauges as opposed to dummy lights. No cupholders or overhead console (even though I just added cupholders today ) I also have the Chrysler 8.25 as opposed to the hated Dana 35

Once again, all preference

 

I like my 96 but I did put a 8.25 from a 97 or newer and fenders from 97+ as well. I also plan to put the newer front grill, grand cherokee seats, 99 intake and diffent dash lights and backdrops. I dont really care about the obd2 or obd1, I do like the newer interior but Im not picky(it all looks good with mud on it)

 

ive had a 89 limited, a 92 laredo 5speed, a 95 se, and currently own a 98 se and i have to say i loved all my xjs they all had there good and bads

89 was nice but not a fan of the NON-HO motors i gotta heavy foot rev limiters are nice

92 was a beast with the 5speed fastest xj ive ever owed would wrap the speedo in 3rd gear at 4500rpms it had a 3" lift with 31s

95 was my baby got it all stock with 120k miles i put a 4.5" lift 32s beat the **** outa it had to put a tranny & tcase in it tho couldnt kill it didnt like the dummy gauges tho or the steering wheel and of course not havein cup holders

98 SE my current XJ i love it ! had dummy guages but did the cluster swap plug and play so easy me personally i love the newer dashes in the 97-01 xjs & the new consoles i have cup holders now omg haha the 98 is basicly the newer version of my 95 so i hope to get it lifted and all like the old one it runs great nothing wrong with it at all only thing id change was i wish it was a 5speed like my 92 was

thats just my two cents worth

 

I had a 92 limited and miss those nice comfy leather seats.

But I like my current 96 because it's like having all the updated guts like the newer motor where the torque kicks in sooner and the newer seat rails which i definitely need gc seats because the seats it now make my back hurt.

My 92 had character and was my first xj definitely a champ and took a beating.