This little piggy...
Hi, Guys! I've been away for a LONG time...good to be back!
In My professional as well as personal opinion, both feet are equally ticklish. I've been tickling people for ages, and have never encountered feet of different ticklish calibers.
I WILL say, though, that I find different techniques ellicit slightly different, if more passionate reactions. For example, whereas the stereotypical 'kitchie-kitchie-kooo!' wriggly spiders fingertip technique drives some people insane with laughter, steady, long, firm scratches drive them well over the edge. I am told it's WAY too intense to take for prolonged periods of time. This is why it's My favorite technique!