Not to get anal about it, but it truly depends -- keep in mind, neither of the criteria below are deal-breakers, just the sort of clothing that gets me going...
If it's full-body tickling, I prefer either nude or wearing capris or shorts with tank top or other sleeveless top. Swimsuits of any kind, somehow, just don't do it for me. Probably cuz it's just a bit too easy...more fun to unwrap the gift sometimes, e.g., slowly roll up the shirt to expose the tummy, pull down the shorts to expose the hips, remove the sandal etc.....
If it's feet, bare is best or if there must be hose, black. I also prefer tickling feet of fully or partially clothed women, for some reason. Probably because my best encounters had this.