Despite being very similar in many aspects, the Mitsubishi Evo and Subaru WRX STI each have their own legions of loyal fans.
The rivalry between the Mitsubishi Lancer Evolution and the Subaru Impreza WRX STI was always going to be one of the greats. Here was a pair of cars with similar setup, equipment, specs and sticker prices that also competed very closely in motorsports. The companies, markets and production runs might have been smaller, but the Evo vs. STI rivalry had all of the same makings as the Mustang vs. Camaro animosity, and their fans and owners some took the rivalry just as seriously.
The origins of this rivalry are very closely tied to motorsports, and success in rallying probably played a bigger role in this rivalry than any other mainstream car showdown. Specifically, it was the World Rally Championship where these cars would make their names. This was a sport that was changing a lot in the late Eighties and early Nineties. The Group B era had just ended and manufacturers were no longer focusing on all-out fire-breathing dirt supercars. Group A was now the top tier of rallying, and it was the turn of the smaller and less powerful cars to have their day in the sun.
For several years, this was pretty much just the Lancia Delta. But in 1990, Carlos Sainz would win the Driver's Championship in a Toyota Celica GT-Four, the first time the championship had ever been won in a Japanese car. Other Japanese manufacturers took notice, and in 1992, Mitsubishi and Subaru would both unveil their rallying machines. Both of these four-door cars featured 2.0-liter turbocharged engines and all-wheel drive. The cars evolved quickly, with new versions appearing about every year to year-and-a-half, and it wasn't long before they were dominating WRC.
Despite this success, as well as the humble nature of the cars the racers were based on, serious motorsport-focused versions of the cars remained rare. These tended to be treated by their manufacturers the way the old Group B cars had been, where only just enough were built in order to satisfy homologation requirements, and at least at first, they never bothered to export them. Small quantities were sold in Europe, but real full-scale exportation was a ways off. The US wouldn't get the WRX until 2000, and the all-out the rivalry wouldn't hit US shores until the Evo's arrival in 2003 and the STI in 2004.
It's true that interest in both rallying and in turbocharged Japanese sport compacts had increased over the past decade in America. But the cars nonetheless entered a market full of enthusiasts already intimately familiar with every detail of each car. This is part of what makes this particular rivalry so unusual. It is a rivalry which had already been well underway in the US for years before the first car actually saw an American dealership. What's more, once the cars did reach America, rule changes in WRC meant that these were no longer top-tier cars. Sure, they still spent plenty of time in the dirt, but they were no longer at the top.
So for the US market at least, the rivalry in motorsports and the rivalry in dealerships and at stoplights didn't at all coincide. And yet, this hasn't really lessened the intensity of it all. The internet age has spawned a virtually limitless capacity in people for arguing with strangers, and a rally-oriented Japanese equivalent to the Mustang/Camaro rivalry was going to spark heated debate whether anyone involved had ever even seen one in person or not. But competition between automakers is always a good thing, and when it's on the internet instead of the street, it's easier for said automakers to be aware of it.
This fact also allows for them to better tailor their products to their markets. Of course, competition is always best when there's a way to take it to the street and settle it once and for all, but longer after the Subaru Impreza WRX STI and Mitsubishi Lancer Evo fell off their perch in rally racing, they would continue to be favorites among tuners and boy racers alike.