regs in order ish
Genesis GS2000-first reg bought, currently being used by one of my buddies. It was cheap and came with some other gear I was needing so no regrets there. Don't have it, wouldn't purchase that particular one again, but it's a good reg. Sold it pretty quick and never actually used it myself because I bought the regs before I got a screaming deal on some PST HP tanks that were 300bar DIN.
Apeks DST/ATX50's-Bought those so I could use my newly purchased tanks. Sold probably 6 months later because I got a good deal on a set of sidemount regs and sold these for what I paid for the sidemount regs. No regrets with these.
HOG D1 set referenced above-sold to a buddy because I'd switched to Poseidon's and wasn't using them. He needed a new set of regs, liked these, and I think I sold them for almost what I paid for them.
Apeks Tek3-got a screaming deal on them, promptly sold, didn't like the first stages.
After those it gets a little convoluted and I can't really remember the specific order.
I currently own
5x MK25 first stages, purchased cheap for hose routing in sidemount. 2x in use with sidemount, 2x on rebreather, 1x with my FFM
2x MK20 first stages, same as above, using for doubles with Jetstream seconds
4x MK10 first stages for same-these have 109 second stages on them
somewhere around a dozen Poseidon 3790's that came as parts of screaming deals with Jetstream seconds and a couple 2960's that are used for stage/deco bottles.
No regrets on any of them
Argonaut Kraken for a few reasons but am using it for my primary single tank rig
In terms of my favorite regulators, I think the Poseidon Xstream MK3 is the best reg on the market, just wish they were as cheap as the Jetstreams