Octatrack for me, mostly due to being able to utilize effects loops via the cue outs and inputs for endless mangling and resampling. I dont think i’d care much for any of my synths without it since I process the hell out of them with it (I just don’t get the same joy doing this with a computer). I’ve always been most creative with samplers and the OT is king for me. I don’t know where my music would be without it.
Second is the Monomachine. I get the most intriguing synth sounds with it… sometimes. Other times I wonder why I love it so much, but that always goes away with the next sound I stumble upon. The key to the MNM for me is using external effects. Sounds wonderful once I start mangling it in the OT.