TTD PTP or ePTP is good for point to point link where link distance 30 Km?
ePTP mode will offer lower latency in ideal conditions. You may be limited to 20Mhz or less channel width though, I don't recall what the distance limitation is at 40Mhz for ePTP mode.
TDD PTP mode will allow you to use GPS sync, if needed, and define a duty cycle to the link. Both modes will work fine for a PTP link, the TDD PTP mode will add some latency though.