I did YC in 2012 and am in Techstars NYC currently with a new company.
YC's reputation is probably 2x stronger than Techstars, but that doesn't directly translate to a 2x higher value-add.
Both programs are a lot different and will jumpstart your company. They've both been 100% worth it.
Note: Techstars programs between cities can be dramatically different (different people running each city), so I can only speak for Techstars NYC.