Well the square format doesn't really say anything to me, the other 2 seem to have a reason/dynamism. horizontal reaches within the art historical canon and the vertical one i think goes against that in some way. personally i like the horizontal cos i think your painting needs to play very subtly with the conventions of painting and this way seems to be the right balance for this piece, it also has a certain grandeur to it which i like. but the decision is yours.
as for whether the putti should be dropping something, well i'm not gonna answer that. whats your game sunshine, do you want to make the photoshop a great piece of art or the painting? cos if you want it to be the painting then you aint gonna find the answer before you start to paint. the fact that you're mentioning it seems to answer your own question for me, then if your not satisfied with it change it during the process, no amount of procrastinating over what it could contextually mean is going to give you the answer, that comes from a gut feeling, either through experience or an innate sense, kind of like the final piece of a jigsaw has been fitted, then you'll generally find the context/concept is the right one.

oh and the turner prize is held in liverpool this year so perhaps you want to come and see that, its open now and i have not much life so generally i can be free most times.