i want to learn performance testing.So please can any one suggest me which tool is better either?

It is very important to understand the concept of Performance Testing like -What is Performance Testing, Why do we automate Performance, Understanding the server -client architecture. After,that you can move to tool like Silk Performer, Jmeter or Load runner.

Learning tool is not so difficult but understanding the concept of performance testing and its requirement is the most imp part as every time while working on tool or as a performance tester you will require the concepts.
All the tools are same in means of recording, execution, No of Virtual users, parameterization, correlation etc but the look and feel is different of each tool.

Now Talking about tools
Jmeter
If you are just learning, I'd go with Jmeter since it is free. Once you have the basic principles of Performance Testing down, then maybe look into other


Borland Silk Performer
It delivers realistic, dependable performance tests across the latest technologies by simulating loads and network speeds for web, enterprise, and mobile applications.
http://www.borland.com/products/silkperformer/

HP Loadrunner
This will give you some of the basics for how to record and correlate your application. There are lots of detailed manuals and online help.

Grinder
The Grinder is a JavaTM load testing framework that makes it easy to run a distributed test using many load injector machines. It is freely available under a BSD-style open-source license.

NeoLoad
NeoLoad is a load and performance testing software solution designed for web and mobile applications, which realistically simulates large numbers of users and analyzes your server behavior.

http://www.neotys.com/performance-load-testing-tools.html

But I recommend that use silk performer first for better understanding then use Loadrunner and then Jmeter.