I dunno about leaning back, but the bucket seats in my 91 are super comfortable and the buckets in my 88 are pretty good too. Can't vouch for the other years and all the bench seats pretty much suck.
My MJ actually has a couple more inches of headroom over my 96 XJ, which is a combination of the higher roofline on the MJ and the shorter old-style buckets (in 95 or 96 they changed the seat brackets around in the XJ and lost some headroom.) Given the choice between an MJ, a mid-90s and earlier XJ, or a mid-90s and later XJ, I'd take the MJ any day of the week if headroom was my only requirement, and I'm 6'4".