I have a boxwood, and just got a Japanese holly, and I'd actually guess it's the holly. The leaves are much more narrow and vertically inclined. Unfortunately I pruned back the only buds on my holly before they flowered so I can't compare on that score. The branches of my ilex crenata are much more leggy and flexible than on my boxwood.
I'm also pretty inexperienced so far, so I could be wrong. But I'd guess Japanese holly.