Most of our clients are usually on the S side of the SMB space, so Salesforce and Dynamics might be too feature rich.  However,  if you want to see an objective comparison between them, this is a good chart that found me in a private forum for Act! Consultants.

We have taken on Zoho, WiredContact and Hatchbuck as our answers to Salesforce and Dynamics for small business owners that want solutions in the Cloud.  For 1/3 to 1/2 the price, we can deliver similar functionality.

Can Act! work here too ? Sometimes.  It just depends on the client’s requirements.