Stock HHKB is better than stock NT
Silenced NT is better than stock HHKB
Silenced NT feels better than silenced HHKB
HHKB layout/keyboard ergonomic/shape is better than NT
NT has more keys (clusters, f-keys...) while HHKB misses a lack of them
I have both, i prefer HHKB overall because i like 60% more than TKL, the HHKB layout looks also better to me but silenced NT is great keyboard aswell (in my opinion as i stated above, NT feels more firmly, sturdier in your hands)
Hard choice imo, both are very good (if it has been silenced)