Before I start, I wanna say that this'll just be my very biased, subjective opinion. With these difficulty things, someone's bound to disagree with another. I have played through all of these concerti, but Tchaikovsky and Rach 1 are not something I'm practicing, so what I say will just be my impression of the pieces. Okay, here goes...

First, what I think about each concerto as a whole.
Rach 2: This is the concerto that I have the most experience with (Finished the 1st movement, learning the 2nd and 3rd). This, to me, is the most mature out of the concerti. (some will disagree and say the Tchai is more mature, but I think the Rach 2). Rachmaninoff said that it was more uncomfortable than his 3rd concerto, and I can see how that is partially true. The technique in this concerto is sometimes unorthodox, and you really have to be able to balance the textures extremely well. I find that the technique fits into my hands pretty well after LOTS of practice, but there are some extremely difficult parts that never feel right in my left hand. I, like many others, have an affinity with this concerto. Definitely my favorite out of the concerti you listed. I can pretty confidently rate the movements like this, from easiest to hardest: 2nd, 1st, 3rd. The first movement is less pianistic than the 3rd, but the sheer amount of notes in the 3rd movement make up for it. All three movements are not easy at all, and require a high level of technique to pull off, but I would rate it like that.
Rach 1: This is an absolutely marvelous concerti, esp. for being an Op. 1 (although, I will be talking about the revised version of the concerti, since no one plays the actual op 1.). To me, Rach 2's technical difficulties arose because they simply were required to make the sound that Sergei wanted, but Rach 1's difficulties are sort of there because he wanted to make it difficult, if that makes sense. It's got a lot of youthful excesses, while the 2nd has neither too many nor too little notes. There is just a lot of virtuosity, since it was a young composer wanting to show off. Now, that being said, there are also a lot of musical things being said in this concerto, but I find that they are much more natural to interpret than the 2nd concerto. And, I have to mention the cadenza. It is my favorite cadenza of all time. Nothing can beat it, if it's played right. So, my ranking of the movements would go something like this (easiest to hardest): 2nd, 3rd, 1st.
Tchaikovsky 1: Okay, I have to confess something. I'm almost scared to write anything about this concerto, but I happen to be of the small minority that believes this concerto is overrated, both in difficulty and popularity. I know that many people will probably say that I rank the Tchaikovsky too low, but hey, you asked for my opinion, so I'm going to give it to ya straight. The technique in the Tchaikovsky 1st movement can be very unconventional, and it is hard. I'll give it that. However, I find that the technique is much more traditional than rach, and much, much thinner in texture. Lots of octaves, arpeggios, and jumps, but it doesn't scare me too bad. Just work a lot on your octaves. I think that, if I was playing it, the biggest difficulty would be to make a worthwhile interpretation, not banging the whole thing out, and keeping it interesting, because Peter milks every single drop out of each melodic idea (too much for me.). It has its wonderful moments, but it's a lot of rambling and awkward piano for me. It is a nice piece, but not my favorite, esp. compared to the Rach concerti. Ranking: 2nd, 3rd, 1st.
With the concerti as a whole, compared to each other, I would rank them like this:
Easiest
Tchaikovsky
Rach 1
Rach 2
Hardest
(actually, i'm not sure about the rachs. They might be pretty equal. I guess it just depends on my mood...

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Now for the movements. I would probably rank them differently by next month, or maybe even by tomorrow, but this is what I'm feeling at the moment. Take this with not just a grain of salt, but a whole tablespoon, if you know what I'm getting at. More experienced, knowledgeable pianists than I on this forum will tell you differently, and trust them. They know better.
Easiest
Rach 1, 2nd movement
Tchaikovsky, 2nd movement
Rach 2, 2nd movement
Tchaikovsky, 3rd movement
Rach 1, 3rd movement
Rach 2, 1st movement
Tchaikovsky, 1st movement
Rach 1, 1st movement
Rach 2, 3rd movement
Hardest
Let me know what you think. (I'm undecided on how I ranked the last four...)
~The Farmboy