It’s the colour for me. Lovely greens and blues, plus he English Heritage red flag pop nicely. The blown whites top left and mid centre detract on the mono. Nice composition though, works well.
Fix the sky problems @stanokella mentions in the mono and I'd like it more: the detail is there in the colour version so you should be able to retain it. It makes for a good advert for English Heritage!
I like both but in the mono shot there are some areas of sky that do need attention. Top left is the main one.