xiaoli, in fact agencies have a wider job opportunities because of servicing different companies of different industries. furthermore, HR usually will go thru agency due to many factors. those MNCs advertised on papers are usually for branding purpose, they will not screen thru the CVs since agency will filter the rite CVs for their reviews. they shorten the process for HR.
furthermore, recruitment consultants will 'sell' the candidate CV to HR more better & faster...which means your chances of getting interview / selected will be much higher.
are you going for full time studies or part time? if full time, then yu may as well look for contract which is renewable annually or bi-annually. if you are doing part-time, then get a job with lesser responsibilities...but of coz, pay will be lesser oso lah. =)