At Bulge Bracket banks, such as Citigroup, Deutsche Bank, JPMorgan Chase, and Lehman Brothers, the name of the game was size.

Armed with a big balance sheet, the top advisory bankers in London and New York hunted deals with their boardroom relationships, while also having the ability to offer their clients financing packages.

But this all changed after the financial crisis.

Post-crisis regulations that were designed to prevent risky trading and lending made life a lot more bureaucratic and a lot less fun.

Pay packages and perks were also more tightly controlled.

That is when the exodus began.

Bankers who would spend a lifetime at places like Morgan Stanley, UBS, and Goldman Sachs, quick to start their own boutique firms.

This new generation of boutique banks is nostalgic for the old ways of banking - small partnerships, where a select group of senior bankers mostly own and operate the firm.

Critics of the big banks say this is a superior model.

Risk-taking is likely to be more prudent when partners have more skin in the game.

Free from the shackles of the big banks, where even your every email is monitored by compliance, those succeeding in boutiques say they're having more fun.

And they're once again making tens of millions of dollars.

At the turn of the century, the top five mega banks made about 50% of M&A fees, while boutiques accounted for 15%.

Today, they control anywhere from 30% to 35% of M&A fees.

The likes of Goldman, JPMorgan, and Morgan Stanley have survived the rise of the boutiques.

But for many other famed names in the world of banking, such as the European houses, the M&A game has become more difficult as the boutiques have risen.