I've tried numerous different lames and knives over the years, from cheap to expensive, and have ultimately circled back around to just using the 'naked' razor blade in my fingers. I get a better feel for angles and depth this way and get better ears and bloom on the loaves, although you do have to be careful not to cut yourself. So, this didn't really answer your question, but I guess I'm voting for a straight blade.
Some good answers are in these posts and comments:
http://www.thefreshloaf.com/search/node/straight%20curved%20lame
(That's the URL that you get when you put:
straight curved lame
in the search box, and click the "search" button.)
Hope this helps.
I've tried numerous different lames and knives over the years, from cheap to expensive, and have ultimately circled back around to just using the 'naked' razor blade in my fingers. I get a better feel for angles and depth this way and get better ears and bloom on the loaves, although you do have to be careful not to cut yourself. So, this didn't really answer your question, but I guess I'm voting for a straight blade.