I always felt that ticklers would like to experiment just a bit to see where the best places are to tickle. Then they will naturally be drawn to the places with the best reactions. Also, like so many other things, variety makes the world a more interesting place.
That said, susi-sue, I enjoy your topic so much I've delurked to toss in an opinion on the subject. My two favorite places to tickle are the knees (second favorite) and the armpits (all time best place). These areas on a lass are, for me, natures most perfect curves and valleys. (I just love the backs of a woman's knees, and there is rarely a day that goes by that the woman of this house doesn't get, at least, a little poke under her arms.
Luckily, my wife's armpits are her most ticklish spots by far. So, they're often my last target, to be attacked after I really get her wound up tickling other areas. By then I get the most delightful look on her face. Often she can't talk very well by that time, so her eyes open really wide and she shakes her head to communicate. This can touch off my best teasing games.
Like you, it sometimes seems to me that the biggest number of ticklers are also feet people. Don't ever abandon ship, however. There are still plenty of upper body ticklers out here, and many of us can't resist armpits.
Hiram