Well, I've just barely started doing flowers, so I'm not positive, but I think the big thing is whether your tools have a seam. I had the Wilton tools, but the seam would rip my gumpaste. I got a couple of seamless acrylic ones, and they work nicely, but they're pretty big - too big for most things I try to do. I got a small metal one for my birthday that I've used now for lots of stuff.
I have both metal and plastic sets. When thinning petals, I prefer using the metal ball tool for its weight. Some of my metal tools also do not have a plastic equivalent. Mostly though, I use the yellow and white plastic set made by PME.
Yah, I like the ones that PME have also. I still have a couple of my first tools left from Wilton but anything that you need to have weight to they snap in half! So I suggest the PME ones for plastic and miriel is right with the metal ball tool. It frills the petal better if it has a little weight to it. All what you get used to.
Metal ball tools make all the difference in the world to me. Plastic tears the edges of your petals when you try and thin or ruffle. And I have had all of my metal ball tools for 7 years, I broke a Wilton plastic tool, snapped the head right off.