We have a SFDC application and as a functional tester I would like to know what tools can be used to automate the test scripts. Need to test UI as well as the functional requirements of application. Can I use QTP, selenium to achieve this. Or is there better tool given by SFDC?
For automating testing and builds in general, I would try Jenkins: http://blogs.developerforce.com/developer-relations/2013/03/setting-up-jenkins-for-force-com-continuous-integration.html
Which has a Selenium plugin too: https://wiki.jenkins-ci.org/display/JENKINS/Selenium+Plugin
tbh, discussions around automated UI testing always seem to gravitate around Selenium. There are other options, but it is a good place to start.
For fine tuning (not auto) UI perfomance, I would look at using either Chrome or FireFox's built in development tools as well as the View State inspector in Visualforce: http://developer.force.com/releases/release/Winter11/View+State+Inspector