My company is a Software development company.
We planned to use TFS 2010 for our future customers development.
TFS 2010 introduce Team Project Collection in order to split related Team Projects.
So my question is, should i use Project Collection per Customers or should i use a unique Project Collection with a Team Project per Customers which will contains some customer solution projects in it
It depends on how independent your projects and customers are.
For example do you what change set number series to increment within a project, per customer or within your farm? See the following link for some of the implications:
http://blogs.msdn.com/bharry/archive/2009/04/19/team-foundation-server-2010-key-concepts.aspx