Octatrack has the most RAM (80mb), but then it can also stream from the card, which more than makes up for that.
I think most of the boxes have Coldfire CPUs in them, which aren’t particularly powerful compared to modern computer processors, but don’t come with the problem of being obsolete every 12 months or so. If I remember rightly, Digitone has two Coldfires and Digitakt has one
For hardware, unlike with computers, longevity is based on continued availability of parts rather than the specification of it’s CPU or RAM.