Skills and Experience
In an MNC, you are assigned a particular project and module, which you may or may not find interest in. Your skills and experience are restricted to a certain area of the process. In a start-up, you have to do most of the work yourself - planning, requirement analysis, design and development, etc. Thus, your skills increase manifold, you are knowledgeable about every phase of the business, and you have thrice the practical experience of a peer who is in an MNC.
MNCs offer considerable growth - designation-wise, financially, and to learn current methodologies. With a start-up, you grow as a complete professional - you learn the value of capital, human resources, hands-on skills, and end-to-end work experience. Thus, MNCs offer lucrative professional growth, while start-ups offer personal and professional growth.
Facilities and Environment
MNCs have brilliant infrastructure, latest software, state-of-the-art tools and techniques, and training programs. The environment is strict, formal, and professional, and there is less camaraderie between employees. Start-ups have smaller office spaces, basic software, no personal training, and limited facilities, overall. The atmosphere too, is casual in terms of dressing, behavior, and etiquette. There is a familiarity and friendship between all the employees, including the founders.
Most MNCs have a fixed style and time of working, unless you are at the top management level and need to brainstorm ideas. For most employees, MNCs offer a 9 to 6 comfort. For start-ups, every employee has to work impossible hours - at 4 in the morning or 7 in the evening. You have to manage everything yourself; there is no strong shoulder to lean on which is why, you must join a start-up if you are genuinely interested in the work, want to experiment, with not many personal liabilities.
MNCs are reputed and famous - they have a brand value and recognition in the market. Working in an MNC gives you an edge, especially during a job change or recession. Start-ups are unknown, at least in the early stages, since marketing funds are put on the back burner until projects are sorted out. If you quit a start-up, most companies in the market would be unwilling to hire you; your skills have no recognized value, there is less trust factor, and less credibility.
The Much-needed Perks
MNCs offer numerous perks - travel, food, on-site opportunities, foreign trips, global exposure, medical insurance, support for certifications, course funding, ESOP, etc. Start-ups hardly offer any of these perks, however, the ESOP plan benefits start-ups more in the future - if the company advances at a rapid level, you, as an initial shareholder, will receive more stock options than others who will join the company later.
If there are any glitches in the work process or projects in an MNC, you will not be kicked out of your job (unless you are on the bench or are totally unskilled). There is enough job security, you have someone strong to lean on, and experienced professionals who will guide you. But, if a start-up fails, you lose your job altogether. You do not have any reliable senior to turn to for advice. There may be no PF or any other plan, and there is no guarantee that you'll find a job immediately.
Whether to prefer a start-up or an MNC is purely a matter of perspective. It would be prudent to state that a start-up is an ideal option for people who are not very finicky about excellent remuneration and myriad perks in the beginning of their career, and instead are open to learning technologies and gaining experience at the grass-root level. On the contrary, an MNC is a good choice for those who are interested in learning particular tools under an experienced wing, those who have to shoulder a huge responsibility, or the ones, who, if given a choice, would prefer to follow than to lead.