The aspect ratio is *almost* the only reason I shoot square format. (The other is for candid style headshots, so I can be quick and not have to rotate the camera...and I also prefer using a WLF for this sort of thing.) The second I first looked into a square format camera, I was blown away by how easy it was to get a good composition. Everything looks good. The hardest part about square format is that I tend to overshoot (many variations on same basic composition) because of this, so waste a lot of time changing film, and a lot of time looking at contact sheets choosing what to print! It is not uncommon that I will blow a roll of 120 on only two or three subjects when shooting my C33. It is not my favorite ratio for for capturing a highly "active" composition, but over all, I think it is the easiest to compose.
Notice I did not say that square pictures are my favorite pictures to view...simply that the compositions seem to "fall" into place the most easily. My all time favorite aspect ratio is 1.5:1.
I love shooting large format and my new RZ, but I find the 1.25:1 aspect ratio to be very difficult to compose. It seems either too "fat" to me, or like it should just be square. (I guess I need a P3!

) I try to compose shots to fit the format, and *always* compose with the intent to preserve at least two edges as shot, but it is still pretty routine for me to shoot with the intent to crop a bit with 4x5 and 6x7cm shots; either to make it square or to make it a longer rectangle. Not so with 35, 6x6, 645, etc.
As for landscapes on 1:1, I can see it being easier with a wide lens. When I first got my Mamiya, I tried some landscape things with it. I did a really fun landscape project with it, where you step into a cyclorama showing a 360 degree view. However, all of the shots were cropped to fit on 8x10 paper, and I used a prism for the shots anyhow. The TLR was in no way necessary, as I wasn't using any of its unique features. In fact, I would have needed a footstool to even compose the shots with the WLF. I am *not* hauling a footstool to the top of Eagle Rock with me! 645 would have been at least just as good, and probably better, in fact. My favorite formats for landscapes are 645 and 5x7. They are not identical ratios, but both are about the same; a little fatter than 1.5:1, but not as fat as 1.25:1. I don't use the C33 for landscapes anymore (though fairly often for "cityscapes", albeit usually hand held). I use an M645 instead for medium format landscapes.