I know for my money, I've had the FW Duet, and a first-gen Scarlett 2i4. Bought the latter when I was having some trouble on a gig using MainStage; as an effort to troubleshoot I thought I'd try a different interface (turned out the software was just struggling with MP3s). Still, I kept that Scarlett to use in the field so that I wouldn't have to disassemble my studio rig every time I had a rehearsal. I would have click/pop/dropout issues with the Duet in the later years, which could have been driver/new OS issues or could have had to do with my used Mac Pro having some wonky I/O connections that I never figured out. The Scarlett is my main interface for the time being since that's the only one I can easily connect to my new MacBook Pro, but I've gotten used to it. In a pinch on a couple occasions I have used my Mackie Big Knob Studio as an interface, but I try to save that for troubleshooting issues or ease of use if my girlfriend needs to connect her laptop to my system to do some work. The Big Knob definitely seems to color the sound, but I personally think it's a little more exaggerated when doing double duty as the interface.
All that to say, since I'm a grad student in screen scoring now, I think it's time to get a new interface. A lot of UA out there for my classmates, but I don't think I can spend that much yet… especially for just two preamps (see also Apogee's Symphony Desktop and the Babyface Pro)—at that price point, I'd rather try out Arturia's AudioFuse Studio so I can record my stage piano and mics simultaneously, though that would also make my Big Knob a little redundant, but not so redundant that I could get rid of it. So all those things considered, I think the Duet is the ideal unit for my situation. I suppose I can take comfort in knowing that I'd be getting in on the ground floor with it, so I should in theory get sufficient years of support and compatibility out of it.
[ 2019 16” MBP: 2.3 GHz 8-Core, 64 GB RAM, 2 TB; OS X.15.7; LP X.5.1.
Early-'08 Mac Pro (3,1): 2.8 GHz 8-Core, 16 GB RAM; OS 10.11.6; Logic X.3.3. ]