Jack
I've used both Imray and Admiralty charts for the South Wales area and to be honest there is not much difference.
They both show tides, depths, wrecks etc. The differences I have noticed are,
Imray charts tend to be of the same scale so one chart covers an area which is where the next chart takes over. Admiralty charts come in several scales so you can get one which just shows eg Cardiff and Barry areas in detail, as well as one which covers this area plus a much larger area in detail.
The Imray chart I have shows port information better than the Admiralty chart I have eg the pontoon set up in Penarth marina. (This may be an unfair comparison as my Admiralty chart is much older) but from what I have been told Imray charts are designed with yacht navigation in mind, Admiralty charts were originally intended for ships.
On my charts most wrecks are shown as symbols where as on the admiralty chart most are shown as a depth (take the wreck depth from the surrounding depth do get an approx wreck height)
Hope this helps
If you want any more info e-mail me
Osprey