CREATE TABLE table_204_30 (id DECIMAL, "year built" TEXT, "works number" DECIMAL, "wheel arr." TEXT, "gauge" TEXT, "original owner" TEXT, "name" TEXT, "current location" TEXT, "notes" TEXT)

which original owner had the most locomotives ?
SELECT "original owner" FROM table_204_30 GROUP BY "original owner" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "original owner" FROM "table_204_30" GROUP BY "original owner" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1