A lot depends on how you are defining horizontal and vertical. I would regard my old 2 channel 27MHz RXs as having vertical pins, my 2.GHz several channel RXs, where the pins poke out of the end, horizontal.
RXs where the pins poke out through the top are normally straight, and it is fairly obvious which is nearest the edge.
The newer, more compact RXs, where the pins poke out of the end of the case, usually have the board at the "bottom" of the case and the pins have a right angle bend, so the "lowest" pin is the one nearest the edge of the board.