WCW in terms of general wrestling content, match quality, storyline ingenuity, and even risk were all good. Anything to do with class was #1 in the 90s. WCW just felt like a good sport with entertainment. I truly felt that their titles meant more than other titles in the industry at the time because the presentation was top notch and the way Tony Schiavone always referred to WCW and wrestling as a sport, "in this sport of professional wrestling" had a lot to do with how I felt about it. The booking of the cruiserweight division was great and WCW rosterwise was like TNA of today, they had the best roster assembled and everything gelled well in WCW until 2000 came. NWO until this day is 1 of the greatest booked storylines in wrestling history that until this day and age, basketball players can be referred to as the NWO. Until this day we see NWO shirts. It's a testament how great they were.
ECW I would say had all of the above. Unlike WCW, ECW's roster wasn't so huge so Paul Heyman had more focus and was able to zero in on things and give more details to things that WCW's booking committee or WWF's booking team would overlook. Hell if you watched TNA, you can see that Heyman's writing was so good that a feud like Raven/Dreamer can be rekindled over a decade later and it is simple enough for a new viewer to understand and be caught up. And match quality wise, ECW was the first to introduce many styles in the US that the mainstream adopted. Heyman brought in the hardcore, the luchas, you name it.
WWF had story development, story ingenuity, character development, and took risk but it was the weaker of the 3 imo. They evolved Undertaker in the Attitude Era, they created Kane, made Austin, Rock, HHH, etc. Storyline wise, Austin/McMahon was great and they followed through with it for years. the storylines with Austin/Pillman, Bret Hart being anti-American, Pillman/Goldust were daredevil but that's where it stopped. Everything else about WWF in the competition era of the late 90s was tawdry, cheesy, or classless. Wrestling wise in the 90s, the WWE was shit especially the late 90s with the exception of hardcore matches and main events. The undercard in the WWE late 90s wasn't very strong until the 2000s. The product was just pure Russoriffic but back then the shock value mixed in and introduced to the mainstream made it ok because it was new but really it was shit imo. It seemed as if all the matches had interference and ref bumps and didn't go over 3-5 minutes. WWF's strong part was their willingness to do shock value so indeed they took risk in the ring and in storylines. Character development wise, I didn't think Attitude era was that strong outside the uppercard in the late 90s. The year 2000 was different. WWE was well booked in 2000 but in the 90s, the character development wasn't that strong. Mae Young giving birth to a hand? Really? Vince McMahon winning the WWE title. The Odditites, DX's childish antics, a fake Hall & Nash as Fake Diesel & Fake Razor, a Goldberg parody named Gildberg. The WWE in the 90s was good because we look at the good things but for the most part it was a joke. Back then, they threw shit at the wall with all the WWF In Your House PPV's. Fortunately enough, they found something that stuck with the edginess they borrowed from ECW and ran with it renamed as Attitude.