The size of your business is an important input into understanding the best solution.
There are systems designed for large companies and there are solutions designed for small business. For example, a system such as a Cloud-CRM is designed for either a small business or a department in a larger company. These are designed and built ‘from the ground up’ to handle small to large numbers of users.
On the other hand, some CRM systems are designed specifically for large busines. The overhead of these systems is such that it would be uneconomical to use in a small business.
For example, a small Business would not use a Siebel CRM or SAP CRM, but could consider Salesforce.com and Microsoft Dynamics CRM. Some vendors such as SAP have different products such as Business One with CRM functionality to fit into these small business segments.