Speaking as a commercial grower I can say that there is no real right or wrong compost, it depends very much on the application.

Over the years I have grown a lot of different crops, in a lot of different composts, and have even been involved in trials of propagation mixes for the forestry commission. Soil based mixes tend to work better for hardwood cuttings, and those that root freely. After all, layering, stool layering and other methods that take advantage of the aerial rooting of shoots take place using pure soil. My theory is that the growth of the roots is naturally vigorous and therefore you need the extra water and nutrient retention capacity.

For soft tip, or semi-ripe material, peat is much better a substrate. These types of cutting are being forced to generate roots from previously differentiated cells, and are left with a wound at the base of the cutting and where any leaves have been removed. This is a pathway for fungal infections to get in and begin rotting the cuttings. Since these spores are carried in the soil water, it is best to not allow the compost to sit too wet. You are effectively looking for a substrate with a reasonable balance over Macropores which drain freely and Mesopores which the roots take up the water from.

The other thing that is key to a better take rate is reducing the transpiration and maintaining humidity. This is done by covering, usually with milky polythene. Lastly the roots benefit from being heated to around 16 centigrade. This encourages growth in suc a way that the cuttings can establish faster than pathogens can attack and get a foot hold.

So basically if the plants are vigorous (cornus, salix etc) and from hardwood cuttings, a soil based mix is good. Anything else go down the peat route.

Decent prop mixes are invariably:

Moss Peat Based
Free Draining, with something added to the substrate
Lower in nutrients than a traditional potting mix

Some good mixes:

3 parts medium grade peat : 1 part horticultural grit
4 parts medium grade peat : 1 part propagation bark
3 parts medium grade peat : 1 part Perlite, Vermiculite or similar expanded volcanic granules.

In general you don't add nutrients until you pot on once the plants have rooted.

Hope the all makes sense,

Nick