llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch is the hardest word for me
or maybe this 189,819 letter long word: en.wiktionary.org/wiki/Appendix:Protologisms/Long_words/Titin
or maybe this 189,819 letter long word: en.wiktionary.org/wiki/Appendix:Protologisms/Long_words/Titin