Hi Dave,
I've tried many different types of meditation. They all 'work' in one way or another. I quite like group guided meditations/visualisations, if they're done well (there are certainly some that are not), but as a personal practice I haven't found anything better than mantra based meditation (I was taught Dynamic Deep Meditation, but this is essentially the same as what Michael teaches for free with his "Discover Meditation" cd's, and is the same as Transcendental Meditation, without the ceremony).
As you say, there are meditations out there with 'rules' but the truth is that meditation is such a simple thing it doesn't require any rules; that's just various people's/organisation's ways of controlling their 'style' of meditation and trying to make it seem more important/better than others (methinks the ego has got in there somewhere.

)
Hugs
Giles