曜 is one of my favorite kanji to write, even if it takes significantly more strokes than よう. Also, knowing that there's a kanji that goes with the day of the week explains the readings (すい vs みず in 水曜日, for example). It's even fairly easy to remember, since it has 日 in it for "day" and a double ヨ, so it's a long よう sound! Days of the week are awesome! ^_^