owned the EQ-5, still own the SE425,
In terms of SQ, the EQ-5 is generally more balanced and a safer overall choice.
The SE425 is very mid-centric, and has a love-it or hate-it signature. Excellent for classical, jazz, and vocals, but a bit
bass-shy and lacking for electronic/hip-hop and some rock.
HOWEVER, the EQ-5 have slightly annoying ergonomics (no cable cinch, awkward over-the-ear fit) and they also don't
include a case.
The SE425, by contrast, are much easier to fit.
For me, being on the go and on the subway/bus/train a lot, The EQ-5 were just too cumbersome, even if I like their overall signature. If I were just using them at home, I would definitely pick the EQ-5, but ergonomics are huge for me, and Shure (along with Westone) always seem to capture this best.