You can go with professional if it is just for 1 organization, here is more information about different versions.
Microsoft Dynamics CRM comes in 4 versions for installation by a partner/customer; these versions can be highly customized using advanced extensions. The CRM Online version cannot be extensively customized because of security issues.
- Workgroup Edition
This edition is only allowed 5 CALs maximum, it is not possible to add more CAL's. If more CAL's are needed, an upgrade to Professional or Enterprise should be done. Also all the server roles are installed on 1 machine and cannot be separated. You can only create 1 organization in this version and the use of External Connectos is not allowed. This version is ideal for small organizations that can use it with the SQL Server Workgroup Edition and on a Windows Small Business Server.
- Professional Edition
Has the same functionality as the Workgroup Edition except there is no limit on the CAL's. To allow more than 1 organization to be installed or to install CRM roles on different servers you should upgrade to the Enterprise version.
- Enterprise Edition
Has the same functionality as the Professional Edition but without limits. This version is to be used when multiple divisions should be accessing CRM from one platform.
- Service Provider Edition
This edition is actually an Enterprise Edition that is configured to accept Internal user requests from AD and external user requests through IFD (Internet Facing Deployment). This version is mostly implemented by Microsoft Partners that offer Hosted CRM functionality. When letting external users connect to this CRM version through the Internet.
You can always convert from Professional to Enterprise by Upgrading the License in the CRM Deployment Manager.
Source
Santosh Kore CRM Developer
