Depends. My favorite watching live was 25, but when you rewatch them I actually thought 26 was the best. The whole story of Shawn retiring and the image of him doing the throat-slash to be ever-defiant even as he was defeated was pretty iconic, only issue live was not living up to the ridiculous expectations the 25 match left for it.
Going back and rewatching the 28 match it was really pretty awful (no surprise, Big Nose is done) but when watching live it had an insane amount of drama. 27 just had the benefit on being on a craptacular show that left us saying "Thank god Taker's here! Whew, finally some entertainment!" so we held onto that match and savored it, because with Cena and Miz in the main event you knew it would be the last thing we'd have to hold on to.
Personally, this applies to the XXV bout too. It was my first Mania so I vividly remember being really underwhelmed and disappointed by every match preceding Shawn/Taker so I loved it when I first saw it but when I rewatched it a few days later the match was just average. It's probably my least favorite out of the four.
Before I begin, Taker's initial match with Triple H at X-Seven is by far my least favorite of their trilogy so even though it's not be ranked, rest assured it's dead last for me. Didn't like that match at all honestly, I was really bored throughout it. Anyway, I'd rank them like this . . .
I. HBK vs. Taker (XXVI) ~ The best match of the four and I really find this match to be underrated within the IWC. Of course, that's mostly because I'm not in love with the XXV bout like everyone else is and since it's usually unfavorably compared to that, I always that it got the raw end of the deal. I love the story in this match (and the whole leg targeting thing, especially Shawn's moonsault to Taker's leg through the spanish announce table), I love how quick the pace is (really, in comparison to the other three [especially the Triple H one's] the pace here is rapid) and of course, the iconic finish (jumping tombstone for the win) and how perfectly it worked as the final match of Shawn Michaels, my all-time favorite. The show is over, close the storybook, there will be no encore.
II. HHH vs. Taker (XXVIII) ~ I've probably explained this a million times before but the reason I like this match so much doesn't have too much to do with the match itself, at least in the manner I normally grade matches. I love it because of the emotions it elicited from my father & friend who were both watching it with me. It was one of the funniest experiences I've had watching wrestling because they got into and so did I. Just not to the same extent, as I was never tricked into thinking the streak would end but seeing my father celebrate when he thought it was while my friend had the exact opposite reaction was a lot of fun. As Rain Pun brought up, if I watched it now I definitely wouldn't think as highly of it, hell I may even dislike it. But this is a match that was designed purely on emotion/drama, its not suppose to be some kind of technical marvel or even some brutal HIAC match, the match was built up and delivered on the drama of the story. It was one of those kind of matches, unfortunately that means its replay value is relatively non-existent unless nostalgia is enough for you but it wasn't constructed for that and excelled perfectly at what it promised. Here's a little side note, this was initially number one on my list but by the time I was finished elaborating on HBK/Taker II I managed to convince myself otherwise. And I'm stubborn prick.
III. HHH vs. Taker (XXVII) ~ With this little broken base I lie firmly on the, "like it" side. I really like this match essentially because it's just two of the top guys really going at it. Big moves & great spots all throughout, a chair shot to the freakin' head (I miss those), the finish (which was absolutely perfect) & the fact that it really did just feel as big as it was suppose to be. Sure there was quite a bit of downtime but it didn't really bother me, it was utilized well as it really built up to the finish. The rational part of my brain wants to put this over the HIAC (the part wants to put everything over the HIAC) but I can't really justify it when I like the HIAC match better so no more last minute changes to my rankings.
IV. HBK vs. Taker (XXV) ~ I pretty much said all I have to say about this match. It's good, probably above average but it just didn't reach the heights that any of those other matches did. Just doesn't do it for me on the same level it does for everyone else.