I've owned both of those preamps, though not at the same time. I had the 38S for about a month, around 15 years ago. Then I spent about 3 years with the ARC Ref 3, and sold it about 8 years ago.
In my system, to my ears, there was no contest at all. I much preferred the ARC Ref 3, more resolution, more musical, more natural.
Again, that is just my opinion, and I have been known to prefer a tube preamp. Very few SS preamps have sounded natural to me, with Klyne the possible exception.
The 38S stood out to me as a very HiFi sounding unit. It checked many boxes, good bass, good highs, but it never sounded relaxed or natural to me. Could have been system synergy, or whatnot, I can't really recall what else was in my rig back 15 years ago, but I did turn around and resold it rather quickly, and the guy who bought it really liked it, so whatever. That's why they make so many flavors.
That's just my $0.02.