I have the Boye set and love it! I love the number of sizes. And the metal are slick and work up nicely.
I haven't had too much trouble with them coming undone. Only once when I did not have them tightened enough.
I've not tried the Denise set, I think there is a split amongst the community here and it will boil down to your own preference!
What the heck, get both and solve the dilemma!