Hi Anis,

For the modo/zbrush/silo ... if it's 'just' about displacement painting :
Zbrush>Silo>Modo

Zbrush is a digital sculpture (and painting) software, with an unusual interface and a not so easy learning curve. Be prepared to watch/read some tutorials because it's not super intuitive and require some practice to master all the tools available.

Modo is a good poly modeler, with some cool feature like texture painting, correct uv tools and a good render engine. The displace painting is based on the vector displacement technology, and for the moment, it's far to be good ... fine to add some little details, but not to really sculpt. There are some good learning materials too.

Silo is 'just' a poly modeler, with really smart tools on that purpose (really nice retopology tool for example) and looks like the new uv tools seems quite good (havn't test it). The workflow is just amazing fast and easy. The displace sculpting is quiete nice too, sure you can't move millions of polygones like zbrush, but it's really not that bad. I haven't tried displace/normal exporter yet.

I remember there is a cool bird tutorial on zbrush, not sure it will fit your needs

http://www.3dtotal.com/team/Tutorials_3/bird_of_pray/bird_of_pray01.asp