I'm not sure which ones you are talking about (could guess fst/tek3). I have fsr first stages and they are okayish. They are not perfect but do the job. If I was to buy again I'd probably get something different. The scubapro first stages look nice.
It seems to me like any 1st stage with a swivel turret and a 5th LP port on the bottom is pretty much optimal.
I have Dive Rite XT1s for my doubles, which configure pretty much the same as the SP Mk 25. With the bottom ports pointed at each other, my hose routing for doubles and a drysuit is pretty much ideal, to me. Or, it was. Recently, I changed the SPG on my left post to a short hose that I run over my shoulder, alongside my wing inflator hoses. Now, that one hose has a bend in it that I would prefer not to have, but otherwise, they are great. I don't know of any 1st stage config that would work better.