I am involved in front office recruiting and would say that unless your father is someone famous or you are very pretty and smart, its very difficult to get into sales and trading.

Research is easier to get into generally, but if you are looking into bulge bracket, you need a degree/MBA from a top university (Ivy League/Oxbridge) and an outgoing personality. For top local grads, easier get into a local broker and then work like a dog to make yourself a name. Same thing for corporate finance, but it can be real drudgery where you catch only a few hours of sleep a week when deals are on.

Boutique buyside firms or hedge funds may be easier to get into and you could rise and make a lot of money, but don't do that much for your resume. Coming from bulge bracket, its much easier to move around.