Well, apart from my previous easily forgotten phones (most of them were slowly destroyed by my experiments as I practiced soldering and building amps) made by Sony/Philips and such, at the moment I am using mostly ESS 422H, Open back KPH30i drivers mounted in Monoprice shells, cheap Samsung/AKG dual driver buds.
I use BTR5, Hiby R3 PRO, LT1210 based DIY amp, germanium SE amp, building something more, but usually very slowly
I would say that for IEMs I would use R3 Pro mostly as portable solution. I have definitely tried more amps in my life than anything else, because those can be built somewhat a lot easier.