Thanks for your comments. I see you get 400 cores for 3USD/h . Where you optimizing for processing power per dollar? Do you know if the m1.xlarge instances are the best for this use case?
It really depends on the use case. I mentioned m1.xlarge as they provide a good general cluster setup. The mix of CPU, RAM, and disk space should work well for most experiments one might want to perform. m1.xlarge instances also have 1Gbps network interfaces when others in the same price range have 500Mbps -- a vestige of the older generation of machines. Finally, they excel at disk space. If you're utilizing HDFS heavily, newer instances are usually SSD (good) but have 10 to 20 times less disk storage (bad).
For the same dollar amount, you can trade for other specs though.
If you're more interested in CPU / RAM / SSD for example, paying $3USD/h for r3.xlarge gets you 3TB of RAM, about 1.5 times more computing power (same number of cores but more compute units), but far less disk space -- 8TB of SSD.
In the end, it really depends on the task at hand, but your dollar does go quite far regardless!
