There were some changes in 1996; ealier bikes have a different countershaft sprocket mounting system, multi-pce counterbalance sprockets and a thinner cylinder liner.....these were upgraded and improved with some other very minor changes in 1996 and stayed the same until 2007. There were only VERY minor changes from '96 - 2007 including colors and a change to the shifter in 2007 - consider 1996 - 2007 to be virtually identical.
In 2008, there were a plethora of changes; here's my usual Gen1 vs. Gen2 post:Basically, the Gen2 was modified to change the marketing focus towards "adventure riding" from "Dual Purpose".
- better brakes
- better headlights
- more wind protection
- slightly larger forks
- increased wattage for aux. gear
- and a number of minor items like larger spokes, better chain adjusters, etc.
Early Gen2's unfortunately had some issues; bad rings, deep hole issue, deteriorating rubber bits, wiring harness rub through. Mostly resolved by 2010.
- the weight also increased (17 - 24 lbs) and suspension travel decreased (from 9.1 front and rear to 7.9 front and 7.3 rear)
- in 2014.5 the suspension received a welcome increase in both spring rates and dampening....though it is still the 1980 tech budget stuff that Kawi used on these bikes since 1987.
Other than the supension stiffness upgrade, it's basically been BNG's for the past 5 years thought there's been a clutch change (possibly not for the better) and they've changed the forged alum brake lever to a stamped steel one along the way.....cheaper I guess.
Best? well that depends..... best stock KLR? I'd give the nod to the 2014.5+ bike. Basically if your use is pavement biased and/or you intend to keep the mods to a minimum then the Gen2 will appeal to you. ....If you ride more offroad and plan on changes, then the Gen1 starts to look better for the longer travel suspension, lighter weight, more robust bodywork and the ability to run with a completely dead battery.
For me and what I do, I prefer a well modified Gen1. I purchased a 577 mile 2000 model last year and would not trade this bike for a brand new 2016 KLR.
YMMV (and probably will)