I think the first one could do with more texture almost really, it sorta feels like the sort of thing that would look like it'd have textured brush strokes, which I know is a completely different ball game in digital art...but hopefully you get where I'm coming from. It's probably because with art though what I enjoy in real life is pieces that have texture and lots of colour

. It's good though

. Only bit I'm not so keen on is the random black ribbon type thing, I can see there's some dark blue shading on there but I think it should have just been kept a dark colour, rather then going straight into black

.
The second one is very cool, though I don't quite like the cloud look that's beneath the S.
And no one else has said they like the third but it's possibly my favourite just because I love the swirly bits and how it's not like...mega bright in your face, just pretty and lovely

. To me though it'd look slightly better with a might cropped off the left.
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These comments are literally just because I saw someone posting somewhere that the C&C in this area is absolutely shit, so instead of being 'Yeah love it!! =D' and nothing more, figured I'd give more of an opinion. By no means though do I think I'm like...any more talented then you or anything though, what you've produced is far better then what I can do, I get paranoid people are going to think I think I'm better then them when I comment on more skilled work >_<.