Maximum signal transmission from OPAMP output
Without OPAMP, direct driving from PIC

This is the worst option.
2 and 3 will probably have the same performance. Using a buffer after amplification might be slightly better.

Personally, I'd prefer a 4-20mA current loop.
Even if you increase the signal voltage and drive the transmission line with a closed-loop power amplifier, there is still a risk of voltage drop at the end node. And you may not be able to calibrate each time to &quot;recover&quot; the drop. If you drive the line with current, all you'll need is a resistor at the end node to convert the current to voltage.