It’s minis all the way for me for D&D.
I played from about 1994 to 2002 using only theatre of the mind (mainly AD&D, but some other RPGs as well). I found that it made you more reliant on the DM. He was the one that could decide how many Orcs were caught in your fireball spell, or whether the Bugbears were lined up well enough to all get hit by your lightning spell. If the DM wanted the Kobold heading for the alarm to be just out of range of your charging Fighter, theatre of the mind allowed him to easily do so.
When I started running a 3E game there were many feats and combat rules that relied on quite precise positioning. So I switched to using 2d counters (monster artwork printed out to mini scale squares and laminated) on a homemade gridded battle mat.
After a few years of using 2d counters I bought some pre-painted WotC D&D minis. I loved what they added to the game and quickly grew my collection to a couple of thousand minis.
I haven’t bought any new ones for several years, but that’s mainly because I reached the point where for most combats I can represent the monster we’re fighting with an actual mini of that monster. For those cases where I don’t have the exact mini, I can still give a pretty close proxy, rather than having to pretend that the Orc with the axe is a Mind Flayer, and the Goblin with the bow is a Drow Sorcerer. There is just something really cool about mentioning that the PCs spot something flying overhead and then slapping a Huge Red Dragon mini down on the table.
The best reaction I got doing that was during our Shackled City campaign several years ago. The PCs were only 2nd level. They entered a room and I described this strange round creature floating in the air and plopped a Beholder mini down on the table. Eyes immediately went wide around the table!
(FYI, it wasn’t an illusion, it was an actual Beholder they were facing!)
That said, for some RPGs I prefer to use theatre of the mind as I think those games work better for their style. For example, Feng Shui and Paranoia both come to mind as games that work better as theatre of the mind, due to the fact that they are more narrative-style games.
Theatre of the mind means that if the player needs the mooks to be next to a window so he can fly kick them out the window and into the garbage bin below, he can do that. If he needs the drinks cart to be near the stairs, instead of in between 2 tables, as it will allow him to jump on it and ride it down the stairs while shooting out the lights, it now is. No need to let stuff like that get in the way of a cool action scene.