That depends on your purpose, budget and resources?
Informatica, SAS, Oracle Warehouse Builder are powerful but requires large infrastructure to setup and trained staff to use them.
Talend, Pentaho, and CloverETL are open source and easier to adopt and deploy to get things started. The things to look for are:
Features, Adapters ( how many DB they can connect with no customization) , Cost ( be careful as the cost structures are all different- no apple/apple comparison) users and BI support .
Homework before looking: Ho many data sources you have. Local/ global deployment- Internal resources or consultant- you MUST have your own data modeler that understand your data structure today.

Informatica is one of the best ETL tool in market. If you go by numbers of projects go live rate , informatica is way ahead than its competitors. Second best is IBM Datastage with distinctive figures, followed by Microsoft's SSIS & Oracle's ODI.
See complete rating by the most trusted vendor (Gartner) for ETL / Data Integration Tool review...
https://www.informatica.com/in/data-integration-magic-quadrant.html#fbid=-U_Q_C5o_Bx

Hi Prince, good question! Mode has a great article comparing ETL tools. Here are the criteria they used:

• Security
• Data quality
• Data completeness
• Data usability
• Support
• Integrations
• Price
• Additional features
• Application surface area
• Setup

Ultimately, they chose Etleap as their primary ETL provider because it excelled in their top five evaluation dimensions (disclosure: I work with Etleap). They decided Etleap met the required security bar, provided reliable data, had the most complete data, and excellent support.
Hope that's helpful!