What is the best server for RoR ?

Hi all,
I have been deploying my RoR application on EC2 server and most
frequently i get "500 server internal problem ." error .
I figured it out this happens when number of user increase above
10.Could anyone please suggest which server to host is best for RoR ?
As i googled , i got number of options and i don't want to be
testifier for all those.

Thanks in advance