I've always used minis, as far back as when we started playing with the Moldvay Basic Set. Over the years, and many moves, I've lost or "donated" more minis than I can remember.
Nowadays I use almost anything that works. I have a huge collection of Reaper, Games Workshop, and Chainmail metals, and a smaller number of Ral Partha, Grenadier, RAFM, and Citadel (old GW) metals. Some painted though a vast majority are not. On top of that I have a gobload of prepainted DDM, Mage Knight, and Star Wars miniatures. Added to that are the unpainted Reaper plastics (Bones), and unpainted plastics from the D&D boardgames. Tokens, and printed cardstock buildings, assorted things that might look appropriate, such as miniature dungeon dressing and furniture, round out some more "terrain".
When the mood strikes me and there are minis I can't find on the market, I'll even sculpt some minis for my games. For example the Aspis drones (warriors), larva and Aspis Cow of the Slavelords series I sculpted for my conversion of that adventure series for my group. I sculpted a tendriculous and a Gloom Golem for one of my 3.x adventures. A Hengeyokai for one of my players, and since nobody produces a medium sized displacer beast I sculpted one as a fey beast companion.
All in all I will use whatever strikes my fancy for miniatures and terrain.