[Goosegirl]

The soil in our garden was badly neglected before we came so we got some good topsoil then got both mushroom compost and rotted horse manure to add fibre and to improve the condition. Apart from cost, in your opinion, which is the best to use or are they both as good as each other?

[mumofstig]

Mushroom compost often has quite a bit of lime in it.
So unless you have acidic soil, I wouldn't use much of it. Things like Azealeas and hydrangeas, really don't like it 

[Subversive_plot]

If you need more calcium in the soil (e.g., growing tomatoes) it is a good choice.  I'm biased though, as all of my soil is acidic.  I suspect it would be a good choice for brassicas.

With hydrangeas, growing them with raised pH doesn't seem harmful (just my experience), but the plants with normally blue flowers will change from blue to pink (at least temporarily).