I have both Addi's and the Addi Lace. The Lace needles are much sharper and easier to work with, especially when just starting to knit.
I bought my Lace needles so I could do a left twist pattern where you are working in the back loop of the second stitch. Thought the regular Addi's would be too blunt. They've worked out well.
I still like the regular ones, but for fancier stitches the Lace is worth having a second set.