I own both the Delica and the Leek and here's what I think:
Blade steel: Delica--the VG-10 will certainly hold an edge longer than the 440A.
Lock: Leek--the frame-lock is pure genius.
Appearance: Leek--especially the Black Leek or the Rainbow Leek. The Delica just looks like cheap plastic.
Strength: Leek--I'm gonna say that the steel Leek beats the unlined FRN.
Opening means: This one's tough. The Delica's thumbhole is very quick and fool-proof, but the Leek's flipper and Speed-safe is also fool-proof and very cool to boot.
Clip: Leek--the clip is elegant and strong and will not loosen and turn like the Delica's.
Handle design: Leek--the Delica is just a little too short to get all fingers on without being crowded (at least in my hand).
Fit-and-finish: Leek--while both are very well made, my Leek has PERFECT fit-and-finish while my Delica is'nt polished on the inside of the backspring.
Having said all that, I'll add one more thing:
If the Leek was available with ATS-34, VG-10, ATS-55, 154CM or even 440C it would'nt even be a contest.
The Leek is a nearly perfect EDC.
Good luck,
Allen.