CREATE TABLE table_203_688 (id DECIMAL, "category" TEXT, "speed\ ( km/h ) " DECIMAL, "speed\ ( mph ) " DECIMAL, "vehicle" TEXT, "pilot" TEXT, "date" TEXT)

what is the least fastest aircraft ?
SELECT "category" FROM table_203_688 ORDER BY "speed\n(km/h)" LIMIT 1
SELECT "category" FROM "table_203_688" ORDER BY "speed\n(km/h)" NULLS FIRST LIMIT 1