Hi Ajith,
The other thing I noticed with #1, whilst checking the horizon, was that because it is so near the top edge of frame, it seems to be barrelled somewhat, the clouds and horizon on left really tilt down on left, but the rocks on right tilt down on right.
And yet I can also see it looks like you have had a go at straightening already on #2 and #3 (top right telltale). If you do this you need to finish the job and if that leaves you with a little transparent triangle which you can't crop off for compositional reasons, just clone in some adjacent sky - it doesn't take long.
I agree with Colin the general landscape composition is best on 1 and 2, but I quite like 5 and 6 too.
If possible, I'd prefer them all at a 680 width to make the most of the space, 500 is a bit titchy for my eyes. I suspect 500 is the default width, what's the next size up, a 1000? If you used that it would limit to 680 and we could see bigger if need be.
Also, as Colin says, if the weather's not playing ball, you're sunk!
Thanks,