I would go with 16GB+ if you are considering storing and transferring large files (Music, games, video) But if you just need it for school or work documents 8GB should be more than enough.
thank you guys for your suggestions but i mean to say that is there any technical issue with higher storage capacity pen drives?I also want to go with higher capacity of pen drive drive so that it would be easier for me to transferring larger files but somewhere i heard about the disadvantage of these higher capacity pen drives.