First miniature(s) you used for D&D.
Our first "miniatures," if you can call them that, were buttons. The players picked from among the fancier ones for their characters. The plain old plastic ones, I painted numbers on them with a toothpick dipped in model paint, and they were the monsters. It worked pretty well, too. None of them ever got knocked over, and it was easy to keep track of which monster had how many hit points left.
I think we used some small plastic dinosaurs for dragons and really big monsters.
Real miniatures didn't make an appearance in our games until much later, when we finally discovered a store that sold them. The first ones we bought were a pack of three dwarves, a pack of three fighters, and my personal favorite, a "young adventuring wizard." That was what it said on the package, anyway. I liked him because he was not at all the D&D magic-user stereotype. He didn't have a beard, nor a pointy hat, or a hat of any sort for that matter. He wasn't dressed in voluminous flowing robes, or a cloak and cape, or anything classically wizardly like that. No, he wore boots and trousers and a loose-fitting shirt with a vest over it. He looked like he was outfitted for a hike. He stood slightly sideways, looking over one shoulder, with his arm and forefinger extended, pointing at something he had spotted, or perhaps the target of whatever spell he was casting. In his other hand he held a wand.
I eventually acquired a fair collection of minis, including a few dragons, a griffon, and even a beholder, in addition to various characters, orcs, and goblins. These days I really like them more for their form than their function. When it comes to setting up a combat on the tabletop, buttons have the advantage.