US vs City

I’m drawing up a short-list of the firms to target for a training contract. I’m planning to apply to the top 10 City firms but was wondering if I should also add some US firms to my list.

If so, which ones are the most reputable and what about some of the new entrants to the market such as Sullivan & Cromwell, which is offering a £50,000 starting salary? Does that mean they will work me like a slave?