sagar, welcome to MobileRead!
Harry is right in what he said about 6"-ereaders and pdf files, as most pdf files aren't made for the size of ereaders but to fit A4- or letter-size-pages.
If you nevertheless insist on buying a 6" ereader because they are much cheaper I would advise you to have a look at the iRiver Story HD which has the best resolution of all and manages pdf files quite well. But I don't know anything about availability and prices in India.
Your other points - eink, good storage, transfer to PC - shouldn't be a problem for any ereader.