I stay in delhi ,which data card should i buy ,and what Kbps indicate ?

i need a data card ,please suggest some cheapest one with tariffs. i do a lot of downloading (7 GB /week) so i need good plan with high speed.and also what does Kbps and Mbps indicate(i found on internet they indicate 3.1 Mbps as speed ) . are they KByte /Mbyte or they indicate Kbits/Mbits