In my opinion, joining startup is good for IT freshers. Where they will get to brush up the skills, exposure in various roles and responsibilities.
Even though salary may be as low as 5-6k, in long run if you are good performer you can earn 25-30k average or after two years experience if you do a job hop you can ask for very high pay. Probability of getting jobs also better as you will have wide exposure and versatility.
If you join MNC your exposure will be limited to one particular project or technology. Sometimes 100s of engineers in a team make less learning and more competition. Internal politics, favoritism, all games which people play to get promotion or good project.
It takes 5-6 yrs to reach middle level or better pay. By the time start up people will be in top position.If you have long term goal and desire to learn more go for startup. Or else go for MNC.