Good evening,
I'm leaning more and more towards the Devonshires. 2nd batt was in Egypt until 1914 however I don't think they are regular soldiers. Look at the trousers of the seated man on the right. His trousers are a good 6 in too long and have been folded up inside and sewn. The chap on the left also has a small part folded up inside. Regulars would have had properly fitted uniforms, especially pre war.
Several of the Territorial batts served most of the war in places like India and the middle east. From Egypt to Iraq so they are all good possibilities.
The new army batts all spent the war in france.
John915