Which is faster? Flash or Silverlight?

It depends. Flash/Flex is faster when it comes to graphic rendering, but Silverlight is faster when it comes to pure computation speed. Here is why:

There are two speed benchmarks for RIA applications, and they both focus on UI rendering:

• BubbleMark: it displays many bubbles floating around the screen as fast as possible. We use the resulting frame per second as the result of the test
• GUIMark: similar to the BubbleMark, but with more effects and animations used: vectorial images, alpha transparencies, text reflow and so on.

Another benchmark that has been developed, CountingPrimes, focuses only on pure computational speed and measures the time taken to compute 10000000 prime numbers.

From a quick look at the figures it seems that:

• Flex is way faster than Silverlight when rendering complex UI.
• Flex and Silverlight have pretty much the same speed with just animation.
• Silverlight is almost 4 time faster than Flex in pure computation speed.