I am looking for a good example of powershell script for SP2010 with which I could activate my features with prior check if feature has been deployed (some are "web" and some are "site" scoped. Could you please guide me or provide some samples.
A really good explanation is already been given on this blog, so I would suggest you to look at it
detect if a feature is deployed or not
Code of checking if a feature is activated or not
Powershell script to check whether SharePoint 2010 Feature is activated for a particular Sitecollection
SharePoint 2010 Deployment: Powershell Script Feature