All of them are in Central London (Zone One). I will suggest you take the open top bus which charges you GBP18 /person. within 24 hrs, you can get on the bus and get off the bus all time in each tourist attractions. It will takes all over the attractions in London.
London Eye charges you GBP 17.5/person, I suggest you reach there at 10:00am that not too much people getting into one eye. The no. of people may be 8 or 18 difference.