Reference: http://answers.ros.org/question/191962/state-estimation-and-localization-in-robot-navigation/
robot_localization -> 3D tacking based on Extended Kalman filter with mulitple sensors (multiple odom and multiple IMU..)and provide more functionality
robot_pose_ekf -> 3D tacking based on Extended Kalman filter fusing wheel odometry, IMU sensor and visual odometry. For tracking pose.
amcl -> 2D localization based on particle filter uses odometry and laser.
Checking further