I used to use NSI platinum forms which I liked but they were fairly expensive.
I now use the INK London forms, originally because they come in a 300 and a 500 pack (and an even bigger pack but I cant remember the exact number). I find they stick better than the NSI ones and prefer the shape of them for application.
I usually find in the hotter months the forms don’t stick as well, usually because people’s hands are a little sweatier. I’ve read on here that some people wipe over people’s fingers with some alcohol to help them stick, however I just apply forms to one hand, apply acrylic then repeat if I find they’re sliding around. X