If you are curious about whether Blocks is better than Panels in terms of performance then check out this post:
http://www.codeenigma.com/blog/performance-panels#comment-4855
This is great. It tests both components and gives the data in a nice, clinical summary. The long and short of it is that Blocks is SLOWER than Panels, especially if you are using Views. But check out the post for yourself.
Thanks to Greg Harvey for doing ALL the heavy lifting on this one!