Travelling by bus is the cheapest.
Travelling by car is the most comfortable.
Travelling by train is the most boring.
Travelling by plane is the fastest.
Travelling by ship is the best .
Travelling by bicycle is the most exciting/
Travelling by motorcycle is the most dangerous.
Travelling on foot is the slowest.
Travelling on horseback is the most uncomfortable.
Здесь на самом деле можно выбрать что угодно из последнего столбика, думаю ограничений нет.