my money no object deco reg is a Poseidon Xstream Duration MK3. Super small, integrated OPV if you put an inline shutoff on your deco regs, really simple, and a lot less violent of a gas path than most first stages. Reg is reversible if you like to put your deco bottles on the right *which I do*, and the breathing is super nice. They are also very difficult to get to start freeflowing which is a common issue when on DPV's with "normal" looking second stages.
I do have one of the balance pistons that was linked above and used it on my deco bottle, but it sticks out a lot from the valve and I don't really like that. It's fine for me in a cave because I drop it and don't have to dive with it it, but isn't what I would choose. They are the same as the ones from DGX since I know Stuart likes them, though I do prefer supporting Randy when I can but he doesn't have deco bottle packages using that first stage. That one is basically the same as a MK2 and with how expensive MK2's are new and how annoying they are to find used in DIN, I wouldn't personally go that route. It is no longer on my deco reg now that all of my Poseidons have been O2 cleaned and is being relegated to one of the regs for my FFM for IWR.
The thing with deco regs is the first stage doesn't really matter, but you NEED the second stage to be good because you're on that reg for a LONG time so it isn't the place to cheap out on your second stages. The discussion about "balanced vs. unbalanced" because you're shallow is wrong. These are all depth compensating first stages so the breathing at depth is the same as at the surface. The IP changes over tank pressure though so you'll probably want a balanced second stage.
I use a Scubapro 109 on mine for extra differentiation from my Poseidons but I would swap it for an Xstream if I come across one on the cheap. I use O2 cleaned Poseidon 3960 first stages on my deco regs because they're small, have integrated OPV, and easy to O2 clean since I have the o-ring sizes for them etc etc.
So, what would I do if I were budget conscious?
I'd buy this, chuck the other bits, rebuild and O2 clean the MK10 which is super easy and Stuart is a scubapro tech anyway, and call it a day
Scubapro MK10 DIN G200 Regulator with Octo, Gauges and BCD Hose - Complete Set | eBay