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.
Thus, MNCs offer lucrative professional growth, while start-ups offer personal and professional growth.
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.
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.
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.
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.
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.