With the introduction of a...
With the introduction of a more powerful six-cylinder, the Jeep group decided to bring back a name from the past: Renegade. Back in the early 1970s, AMC offered a Renegade package that got you a V-8 in the CJ-5. In Jeep people's heads it lived on as the rip-snorting fast-as-hell Jeep that was almost scary to drive because of its low curb weight and the V-8. Well, today, the Renegade name is forever tarnished, thanks to this YJ (not to mention the laughable KJ Renegade). Under the fiberglass is largely a normal YJ with a few more holes in the sheet metal, so all is not lost. If it's in great shape and a good price, nab it and strip the fiberglass off of it.
'91-'96
The '91 model year saw the introduction of the High Output 4.0L engine, and gone were miles of vacuum line. This motor is reliable as an anvil, puts down decent power, and the fuel injection system has proven itself to be largely trouble-free, proving all the fears of the computer-controlled system unfounded. Meanwhile, the four-cylinder also benefitted from multi-port fuel injection and a resultant bump in the power department. An unfortunate side note to the '91 model year is the Renegade, which was basically a $5,000 tree-and-rock grabbing fiberglass fender and bumper package.
Crash standards for the '92 model year meant that the triangular roll cage that had carried over from the CJ-era was modified and squared-off so that the rear-seat passengers also received three-point seatbelts. Also gone was the center-dash analog clock; instead, a 4WD shift indicator light showed up to stay, and the cable-driven speedometer took a bow in favor of an electronic speedo. In 1993, more government involvement led to a high-mounted third brake light. Drivers who forgot what following distances were led to Jeep offering an optional ABS system on a Wrangler for the first time.
By the time 1994 rolled around, Chrysler finally addressed one of the problems that plagued both six- and four-cylinder YJ owners through the years: that dang hydraulic throwout bearing. Finally, the Wrangler got an external master/slave clutch setup like it should have had from the beginning. Another bright thing about the '94 model year is that due to staggeringly low sales, the Renegade made its last appearance in the options list.
Some will argue that 1995 was the last year for the YJ, some will argue 1996; we've never seen a titled '96. Though the TJ came out in late 1996, all were titled as '97 models. Regardless of splitting the year hair, the last YJs off the line are arguably the best. Many of them benefitted from the larger 297x size front axle U-joint. Some of the last YJs got the TJ-style rubber windshield rests instead of the U-shaped style that ran for 40-some years, and the later YJs off the line got what many refer to as heavy-duty cast aluminum tailgate hinges instead of the stamped steel hinges that were on YJs from the first. While less likely to bend, the aluminum hinges have been known to lock up in rusty climates and become very difficult to open. We have even heard of some of the very last YJs getting TJ-like rear bumpers, and while it is entirely possible thanks to both models sharing rear crossmember stampings, we haven't personally seen it.

From its introduction in 1988...

From its introduction in 1988 through 2003, the Sahara was the flagship of the Wrangler line. In 1988 the package included a 113-amp alternator, a higher CCA battery, color-matched steel wheels, a special Sahara-only exterior color with body color fender flares, and Sahara-only interior. The interior featured front seat-back pockets, roll-bar padding and carpeting was standard on the Sahara. Hardtop models got tinted glass standard. It's likely that the alternator and battery are long gone, so if you are looking at a Sahara, all it has is hard-to-match seats and a sticker package on the exterior.

Aside from the roll bars,...

Aside from the roll bars, the center dash gauges are an easy way to tell what year YJ you are looking at without hunting the owner down. Shown at top is the '87-'91 dash, and below the '92-'95 dash. The absence of the clock means that there is an electronic speedometer...

...That translates into easier...

...That translates into easier speedometer recalibrations and the ability to easily upgrade to aftermarket electronically-driven gauges. No need to go buy a new speedometer gear every time axles, gears, or tire sizes change. Just get an aftermarket programmer and you are good to go.