1)repeater is faster then gridview.
2)repeater is faster then gridview because it is all html 
based and it does not produce much unneeded xml. There are 
more reasons for it..

Repeater
  

Repeater is okay if you need to show data from some data
source. It offers the basic rendering options: header, item,
alternating item, separator and footer. It is really up to
developer how to fill these templates. By example, it is
easy to use Repeater to show read-only lists using templated
elements.
  

Repeater is faster because it offers only basic data bound
control rendering functionalities. If you want to show data
and you don't need any complex features described below then
repeater is the right joice.
  
GridView
  

GridView is rendered as table with columns and it is created
to show data and let users to manipulate it. GridView offers
powerful built-in features like:
  

    * events for sorting data when user clicks on column
heading,
    * row selection,
    * row operations like adding, editing and deleting,
    * paging,
    * command columns and events to handle the commands.

  

GridView is excellent choice if there is a need to show
tabular data and also provide users with features described
above.