What are the best Database as a Service available in Cloud ?

Microsoft SQL Azure Database

again boys always see what are the requirment

what applications what scenarios what budgets many things to consider before saying any thing is best or not. i have many others by which i know i can have multiple backups of DB in multi continents for the same or even less what you have to pay for azure

lots of considerations boys

always think before you say

for me; msSQL on windows Azure

As Aqeel said what would you like to do and what exactly you are looking for. Who said it needs to be an rdbms you might need nosql database or may be you need something totally different with a totally different architecture

Why not use AWS (Amazon Web Service) RDS solution for SQL Server.