What is the difference between LDP and RSVP TE?

Ifyou need is to set up LSP, use LDP. If you require traffic engineering and resources reservations in MPLS core, use RSVP.

Nowadays, most people use MPLS for its great traffic engineering capabilities, so my fair guess is that RSVP-TE is the most commonly used signaling protocol for MPLS networks. But LDP and RSVP-TE can be used within the same network: LDP setups LSPs based on routing data, whereas RSVP setups additional traffic engineered LSPs.