Who is tougher the US Marines or UK Royal Marines?

Tough question, and not designed to improve Anglo-American relations, so I'll have a Walfdorf Salad and say that both are very tough, and I would not want to get on the bad side of either. The US Marines are a much larger unit than the UK Royal Marines, but the US is a much larger country, so it may come out much the same in terms of individual toughness.