I had to go with WCW/nWo Revenge. It was the superior N64 wrestling title.
Everyone who says No Mercy must not have had a copy as screwy as mine were. At random times, the game would glitch and all the created wrestlers and unlocked wrestlers were gone. After putting a lot of work into creating extra wrestlers and unlocking the ones on the game, it always pissed me off that the friggin' thing would glitch. And, I had a few copies of No Mercy, and every damned one of them did it. Just off of that (and the horrendous slowdown during Ladder matches, Rumbles, and Fatal Four Ways or any time more than three weapons were in the ring) No Mercy isn't even close to "the best."
Besides, No Mercy didn't offer anything really new besides the Ladder match. Everyone talks about it like it was the second coming of Christ, but it wasn't that good. In fact, with the minimal additions (and the loss of full entrances), I see No Mercy as the most overrated wrestling game to ever come out. Save a couple of bucks and just buy WCW/nWo Revenge, you get the same amount of fun, and a better roster to boot.
Yeah I had a messed up No Mercy as well. Returned it for a new version....same crap.
But what about Wrestlemania 2000?
It had a huge roster, the same engine as No mercy and WCW/NWO Revenge (Although you could do a run-grapple in No Mercy) had a great campaign mode , and a Create a Wrestler feature.
All 3 are great games, but my vote (Of these 3) goes to 2000 (Only because No Mercy was all glitchy)
Recall the N64 wrestling game evolution.
First Came THQ with WCW World Tour. A fun game with few bells and whistles.
Then Akklaim with WWF Raw is War. Many bells and whistles, a fun game, if you consider 8 button combo's to do a single move (And the button combos were different for all the wrestlers) fun. Also there was the CaW mode, which was very cool at the time.
THQ then followed up with NWO/WCW Revenge. Slightly revamped version of World tour with NWO guys in it. A lot of fun, still no CaW (Although you could rename characters, and they had alternate costumes) and the campaign modes were simple.
Akklaim came out with a followup to RAW is WAR. I saved my money because rumor is it was pretty much the same.
ECW had a game at some point. Never saw it, rumor is, it was bad.
New, THQ took over the WWF license, and made WM 2000.
Caw, Full campaign mode, all the things you loved about WCW World Tour and Revenge were here (Except the WCW wrestlers who hadn't jumped ship yet...Jericho and Show were here), 4 costumes per wrestler, battle royal play for when the guys were over and we were waiting for a quality WWF PPV to start (I'm serious....back in the day when I gladly paid money for WWF PPVs this was part of the tradition....the joy of throwing out your pal who was playing as Triple H only to have him come back as Pat Patterson, Mae young, Chyna or X-PAC....oh how we'd laugh at him then). For my money, the greatest wrestling game at the time.
The final 2 N64 games were No Mercy and WCW Backstage assault.
Never played WCW BA, but again, word was it was bad. As for No Mercy, well THQ had this track record... each game they made used the same engine, with the same easy to learn controls, and each game added to the previous one. And honestly, if not for the bug chip (n64 games were cartridges, so they had built in memory, so when youcreate a wrestler, unlock items, win belts etc. it is saved to the cartridge. Such was teh case for all the previous THQ wrestling games. On No Mercy a bug in the chip would cause it to wipe out all data from time to time. Custom wrestlers, unlocked items/wrestlers, campaigns complete....all gone.) this would have been the top of the heap. But alas its hard to get into a game when all your progress gets wiped out (And not even just when you turn it off. In the middle of a game, you finish a match and go to menu screen, suddenly it all gone.)
When Nintendo came out with Game Cube, THQ kept the WWE license and made several more wrestling games....
Wrestlemania 18. THQ may have been the distributor, but a different developer (AKI was the N64 developer) made a game that I found pretty much unplayable (Horrid controls).
Wrestlemania 19 brought back the familiar simple control model that N64 games had...but the game's campaign mode was bizarre. This game was made around the time of the Alliance (WCW/ECW) Invasion of the WWE. So the storyline is that you've just been fired by WWE, and Stephanie McMahon has hired you to take the fight to your former emplyer. You have timed missions (Matches almost) in various location (A mall, Parking lot, Shipping docks, contruction site) where you have to complete some objective....occasionally facing WWE wrestlers who are trying to stop you. One mission is that the construction site, where they are building the arena that the next Wrestlemania is to be held at, must be delayed, so you have to throw 5 construction workers off the unfinished building. BTW Kane or Matt Hardy might show up to try and stop you. Personally I don't expect a wrestling game when I play Zelda, I don't expect an action RPG when playing NHL 2k6, and this sure as heck ain't what I want from a wrestling game.
Day of Reckoning was next. Pretty good game.
Day of Reckoning 2 was next. Only difference I know of from the first is that now, your character has endurance...so if you tire yourself out, you gotta rest. Suddenly Randy orton has found his niche.
Anyways as for my favorite wrestling game....to date......
WWE Raw 2 for X-box.
WHy?
Open ended Season mode.
This game has an amazing season mode (I've played Nintendo wrestling games, but never a PS wrestling game, so if I'm raving about features on any PS games, that's why). You can plan attacks, and plot feuds on the various cards, or just rest up before a big match. And, I'm over 3 seasons in, with no end in sight. Plus up to 4 players can play in season mode at any time (CHoosing any wrestler on the roster)
And with CaW on Xbox, you can use your own ripped music.
The only thing bad I can say about this game, is the engine isn't as good as some. For the THQ wrestling games, it tracked damaged, so if you worked over an opponents leg for 10 minutes, he dang well had a limp. Not so on this (In fact I've seen opponents pop right up after I gave my finisher....that's not cool)
So to sum up.
Best ongoing wrestling game....WWE Raw 2 for Xbox.
Best "Play with your friends, many of whom don't own this console so you need easy controls and a fun game"...WM 2000/or WCW/NWO Revenge.