Hi Dave,
The best, but most expensive, is the full structure report, but this is best left for properties that you really have your heart set on. So I'd say a homebuyers report would suffice if your still just in the process of looking.
The standard valuation is just a report of decorative condition and minor faults that can be seen on the surface.
I think, but am not totally sure, the Home Buyers report is a bit more in-depth than the valuation, and includes a more detailed survey of the property itself and the area in which the property sits.
The Full Structural Report really speaks for itself and includes lifting of the corners of carpets and a lot of tapping on walls and such like. A good survey to have done, if the property is what you want to live in for a good few years, as it will also provide for a report on the future life expectancy of the structure.
All surveys will include a report of major works done to the property over the years, but you can obtain an extract copy of the forms from the local council planning department yourself, so any property you have looked at so far can be looked at through this method.
Get a good lawyer who works for you, not the ones who desperately want your business, and they'll do all the donkey work for you in these matters. Just tell them what you want and they'll do it from there. You pay for it all in the end any way, so why worry.