Which O/R Mapper for ERP application

[C# Programming]

Hello
I create Enterprise Resource Planning apllication for construction branch.
I need easy to lern, rebuild, flexible and with good performance O/R mapper.
There is many option:
- nHibernate,
- SubSonic,
- XPO,
- Castle ActiveRecord,
- Lightspeed,
- CodeSmith,
- Fluent nHibernate,
- Visual Paradigm ORM.

Probably for begining every orm is good for me but in future when me application grows, not exactly.

Please, share with me yours experiance and let us choose the best solution.
Best regards
Lukas