Which is superior, CSS transparency or PNG Transparency?

Question

Should I use PNG transparency or CSS transparency?

My first instinct is to go with CSS. However I heard somewhere that the filter in IE is slow and that I would get

Answer 1

there are MEMORY LEAKS in IE (including 8) when using png 24 bit! please beware.

http://robertnyman.com/2009/05/26/serious-memory-leak-issue-with-24-bit-png-images-with-alpha-transparency-in-internet-explorer/

I used pngs with some jquery to slide some text and the script is dead slow! I removed background pngs and the script is fine.