Working in a MNC is definitely not a must. Salary wise, i am sure there are SME that can afford to match the pay of MNC or sometimes even higher. Job scope wise, SME might actually expose you to more functions of a business due to more multitasking, one man show type of situation.
However I think the biggest advantage a MNC have over a SME is the brand name. Having that brand name on your resume does help in a way or another.