If you want to learn Performance Testing then you can learn either JMeter or Loadrunner (These two are famous Performance Test Tools).

Earlier LoadRunner was having more market share than JMeter, now JMeter also having a good market share.

If you learn any one of those tools first then it is easy to learn another tool.

If you learn both the tools then your opportunities may be more.

Note: Learning two tools for the same purpose is not mandatory.

Famous Performance Test tools are, JMeter, Micro Focus LoadRunner, IBM RPT, Silk Performer, QA WebLoad, NeoLoad, etc…

Sub-sets of Performance Testing are Load Testing, Stress Testing, Spike Testing, Endurance Testing, and Data Volume Testing.