out of those 3, sony would come out on top. their processor is faster than most other camera company's. they also have a carl zeiss lens which is one of the top lenses you can have. hp cameras in general sucks, well the ones we;ve had at my work anyways.
more megapixels isnt always better. what it'll do for you is give you the ability to blow your picture up bigger. with a 6 MP you'll be able to go into an 8X10 if you want, any more pixels than that just means the bigger you can go with the picture.
in those 3, i'd stick with the sony but if you're looking for something more universal try a canon. sont uses a memory card you can only use with a sony so if you buy another camera and dont want to buy another card, you'll have to stay with sony. canon uses an SD card which is used in basically every camera brand except sony, fuji and olympus.
i sell digital cameras and for most of the consumers i meet,
1.canon
2.sony or
3.panasonic are usually the best options for them.
find a good salesperson who will know how to match your needs to a camera (i.e. - not someone who pushes one particular camera because it pays them good commission). make sure they're asking you lots of questions about what you take pictures of, where, when, etc.
a good salesperson is hard to find. hold onto them once you find one.