Frankly, exit options are quite broad (excerpt of what I remember my fellow alumni doing):
- Large companies (typically after advising the industry), often "strategy department" or in-house-consulting
- Other, often smaller consulting firms (with chance to become partner)
- Private Equity
- Startups (more recently; typically joining funded ones, but also starting new ones)
- Other professional services (HR/recruiting, coaching, ...)
- Academia/think tanks
- Freelance consulting
- Joining/taking over the family's business
Also depends on the major, a lawyer/doctor has other options than a physicist. I remember an internal analysis that physicists stay with the firm longest on average, both a combination of them being the smartest and having (ceteris paribus) the least amount of options compared to other majors.
Regarding startups/PM opportunities - yes, for sure, especially if you are < 3 years with a firm. Short term, consulting helps you with about anything:
- You learn to bring order into complexity, structure things and communicate them clearly, as well as present your work -> universally applicable
- You learn to work really hard and accomplish things fast as part of a project team
- You learn how corporates work and think and how decisions are made (great if you want to sell to them)
- You gain access to a highly valuable network (colleagues and alumni)
- Having worked for the firm is another stamp of approval on your resume
However, these effects diminish over time, and after a certain period you actually become less valuable when you think about going into startups:
- Your salary level gets so high that it is really difficult to find adequate alternatives (took me 3 years after starting my own company to get to almost equal level)
- Your level of entitlement skyrockets (perks, expected comfort level when traveling)
- You forget how to do actual work - you only manage & communicate, and are even further detached from "business reality".
- You focus on learning internal consulting firm things (internal processes, how to sell projects, how to become a partner, ...) which are generally not as valuable when switching careers
To come back to the question (lol), it's not easy to say which is the most lucrative, as it's a combination of risk/reward. Corporate tends to be very stable with limited upside, but also limited downside and better work life balance. PE is paying better, but in the end depends on bonus and performance. Startups are usually paying (way) lower, but you have the upside to hit it big (albeit rare). Actually, freelance consulting is quite lucrative if you find a niche and project flow (lower rates but also almost no overhead cost so everything goes to you) but less sustainable over the long run as you're selling your time but in general don't really build a career.
Hope this helps somehow :)