Hi Lucy,
First off, I just wanted to say that I am offering my opinion/suggestion in a spirit of trying to be helpful, and hope that it's taken that way.
I prefer the second photo, and for most of the reasons others have already mentioned. While I like the photograph, there are two things I would consider weak points, and I have a suggestion for you:
First, the grassline slices right behind your swing, and in so doing becomes a visual distraction when it need not be. Second, there is so much tree trunk in the frame at right that the whole composition is a little "right-heavy" for my tastes. There is also quite a bit of essentially empty space in the grass at lower left, but here I think it is helping balance your composition a bit- it helps counteract all that tree trunk on the right.
However, I have one little suggestion that I think might result in a stronger photo.
Try taking the shot again, but this time from a postition a little to the right of where you were for this one, and also from a little bit higher up (get a stepstool/ladder if need be).
That simple change in your point of view (as I'm envisioning it) will separate the swing a little more from the tree, and will place it a little lower and to the left. This nicely fills some of the dead space at lower left, gets the swing below the grassline and not on it, and will give you less trunk on the right side, resulting in a more balanced, and possibly more pleasing photo.
Again, just my two cents.
Kind regards,
Brian
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Brian
Digital Image Gallery:
http://mywebpages.comcast.net/spiritmist/Brian_G_Digital_Image_Gallery/index.htm
'To quote out of context is the essence of the photographer's craft.'
John Szarkowski, The Photographer's Eye 
