I think that speaking from the heart is better than reading off a piece of paper – but it all depends on what works for you. If you are the type of person who freezes in front of a crowd then it might be better to write something down.
For the speech you really don’t have to say much. My maid of honor said how she had meet me and then she recalled a funny story of the two of us.You could always recall some special or funny memory that you had with your sister. I always like to try and make people laugh – so I would add in a funny story…nothing to embarrassing though; she is still the bride.
Basically all you need to say is that you love her and you wish both of them the very best. You can keep it short and sweet.
Here are a few websites that might give you some ideas…
http://www.speech-topics-help.com/maid-of-honor-speech.html
http://wedding.theknot.com/bridesmaids-mother-of-the-bride/bridesmaids/articles/wedding-toasting-tips-for-the-maid-of-honor.aspx
http://wordpress.com/tag/maid-of-honor-speech-examples/
Good luck!
