I've had an excellent experience at Quadriga Partners. The work is interesting and junior bankers are given a tremendous amount of responsibility from the start. Within the first few months of joining the firm I was directly interfacing with clients and leading deal-related projects. Expectations are high, but the other junior bankers and senior bankers are always willing to help you out when you get stuck. The culture is second to none and is what makes the long nights/weeks/months fly by. The compensation structure is very attractive / above-market. Wouldn't want to do IB anywhere else.
Cons
If you know what you're getting yourself into (e.g., relentless hours, working weekends, frequent travel) then there aren't any.