MD MK1. Bought it used about 13 years ago and it’s been my best mate since. Had it upgraded with the UW kit. Had to get some parts replcaed when it didn’t boot up anymore last year. Jog wheel encoder is acting up now. Will have to repair that. I’d only let it go for an MK2 with UW and +drive.
Bought a used MM MK1 about 10 years ago. I have more of a push and pull relation with it. Didn’t grow on me like the MD did. But could never bring myself to sell it and every once in a while I pull it out and re-discover it.
Lots of of other synths, drum machines and groove boxes passed through my studio since about 2000, only MD and MM stayed. recently started building a hardware setup again by adding an Analog Heat, Novation Circuit Mono Station, Eventide Space.
In the fx department I have an EHX Memory Man Deluxe and a Dynacord Echocord Mini that have been around for very long. Recently added an EHX Stereo Pulsar to the Memory Man to make it a pseudo-stereo ping-pong delay.
My firewire audio interface MOTU 828mk2 has also been with me since I can’t remember when. Reliable and durable. I have an Ultralite mk3 hybrid which is not quite as reliable.