My favorite is Mylo Xyloto. I feel like it's a rarity in music these days to produce an entire album that takes a really positive view of life (Images and Words, my favorite album of all time, is another rare example of this), and I really appreciate that in Mylo. Nothing wrong with sadder music—Ghost Stories is my #2, after all—but I love a well-carried-out positive album and will consistently rate those very high. On MX, even the sadder songs seem to take it in stride, particularly within the context of the album. The album gives off a whole feel of "yes, bad things may happen, we will definitely have struggles in life, but ultimately, life is good and is capable of being a great thing, so when some things go up in flames, don't let it break your heart" (song title puns chosen specifically to fit the sequence of songs that I feel really expresses this theme). Then there is the beautiful upbeat pop instrumentation and the impressive combination of electronic-influenced pop rock with acoustic guitar songs. It's actually somewhat impressive that Us Against the World is a song that feels totally in the proper place fitting in between Charlie Brown and Every Teardrop Is a Waterfall in the album order. And there are just so many good songs on this album! Too many to list, but Every Teardrop Is a Waterfall, Hurts Like Heaven, Us Against the World, Charlie Brown and Don't Let It Break Your Heart are all favorites.
I agree with all of what you said about Viva, and I think that one is a really good album. Personally, I just don't think the songwriting is quite as strong as it is on Mylo—and I realize this is an unpopular opinion! Songs like 42 and Reign of Love fit into that "like a lot, but don't absolutely love" category for me (and it's hard to gauge that because I really like most of Coldplay's songs), and there are fewer songs from Viva that would go in my top 10 compared to songs from Mylo—VLV would get the two title songs and maybe Lovers In Japan while MX would get Every Teardrop, Hurts Like Heaven and at least one and probably two of Charlie Brown, Us Against the World and Don't Let It Break Your Heart. But I totally see why you would like VLV best. It's a really, really good album.
My ranking probably looks like this:
1. Mylo Xyloto
2. Ghost Stories
3. Viva La Vida or Death and All His Friends (with or without Prospekt's March)
4. A Rush of Blood to the Head
5. X&Y
6. Parachutes
7. A Head Full of Dreams
I would consider the top three to be near-flawless albums. All killer, no filler. Especially the top two where I can't find any dips in quality, while I think VLV has some slight peaks and valleys.
Rush of Blood has a tremendous first five and last two songs (and I mean tremendous—the title track and Amsterdam are heart-wrenching), but the four in between range from just decent (Daylight, Green Eyes) to pretty good but not great (Warning Sign, A Whisper). Again, nothing bad here, and a lot of good, but it doesn't maintain the level of quality all the way through that the top three do.
Then there are the last three, which are by far my least played Coldplay albums (the above four are the ones I would quickly reach for, these I would be less likely to play). Parachutes, I know, is a favorite of a certain subsection of the Coldplay fanbase, and I can see why, but this type of songwriting doesn't always include what I love about Coldplay's later works. There are a lot of good songs here—Don't Panic, Spies, Yellow, High Speed, Everything's Not Lost—but some that I don't care for as much. The other two really are the two albums where I feel they didn't move that far away from prior albums stylistically. X&Y is like Rush of Blood 2 and AHFOD is like Mylo Xyloto 2 (featuring slight Viva La Vida). Both have good songs, particularly X&Y, which actually has a lot of killer tracks: Square One, Fix You, X&Y, Speed of Sound, Swallowed in the Sea, Twisted Logic. And AHFOD, while it doesn't have a Fix You, does have Everglow and Up&Up. But they also are a bit same-y, which would be fine if they were on par with their counterparts, but they aren't. From X&Y, only Fix You and Swallowed in the Sea are on the Scientist-Clocks-Rush-Amsterdam tier, and from AHFOD, only Everglow and Up&Up approach the mid-tier MX songs like Major Minus and Princess of China.
So, yeah, there's my dissertation on Coldplay, which I did not mean to be this long, so sorry about that! But I totally understand what you're saying about Viva, even though Mylo is my favorite.
Edit to add a part about Ghost Stories, since it's my second favorite but the only one I didn't talk about: I love Ghost Stories not only because of its emotional weight, but because it sets out to create a beautiful, intimate atmosphere and totally succeeds at doing that. It tries to be music that is very intimate and heard around a campfire, Chris said, but it's a little more than that, because of the electronic elements. But the whole thing creates a feeling of desperation. Desperate love, desperate emotion. And that's really powerful. You hear it right off the bat in the opener, Always in My Head, which begins with the words "I think of you, I haven't slept." That's Ghost Stories in a nutshell. "I think of you, I haven't slept." Go. Make an album about that. And they do and it is spectacular. The album finds a theme and sticks tightly to it, maintaining the emotional vibe throughout while playing on different aspects, different tones. A Sky Full of Stars is the only stylistic deviation, and it's a burst of emotion and after the quiet desperation of the album up to that point. But it's still a desperate song, and it still fits the album. It's just that instead of staring at the night sky in silent desperation, A Sky Full of Stars screams out to the sky and to the world "I don't care, go on and tear me apart." And then it's followed by O, which returns to a similar vibe as the rest of the album and talks about letting go.
Really, it's a concept album. Always In My Head is the introduction, it's where the process of contemplation begins. Magic and Ink talk about the beginning of a relationship and the growing devotion that comes there. In True Love we see that powerful devotion which up until now only had desperation lurking just under the surface ("Want to fall, fall so hard" and "All I know is that I love you so much that it hurts") come out fully. "Tell me you love me, and if you don't, then lie to me"—the voice of someone desperately in love. And we know what happens. She can't tell him she loves him, and she can't lie to him. Midnight is the best song, it is so beautiful, and it is the absolute pit of the album. If you've ever been up late at night and gone outside and looked at the stars, and felt the desperation of the midnight hour, you get this song. Chris gets it and I so completely connect with the emotion that he created in this song that it totally floors me. "When I'm rolling with the thunder—but bleed from thorns, leave a light, a light on." Another's Arms and Oceans cover the pain of the aftermath of the breakup. Oceans is gorgeous and I love it almost as much as I love Midnight. The video of it where Chris performs it on a pier in the Ghost Stories Live 2014 DVD is astounding. Then the aforementioned Sky Full of Stars and O swing comes in, and we find that only by accepting the good and learning to let go can the protagonist recover, emotionally. "I don't care, go on and tear me apart" is desperate, but willing to let go. And then he says "fly on."
I did not intend for this to be as long as it is, but I really love this album. It's a really close second to Mylo, so much that the two could be considered to basically be my co-favorite Coldplay albums.