I don't know, in the Julia/Barnabas kiss .gif they he looks very uncomfortable, or is that the point??
BTW, I think I have read that when they were rehearsing love scenes on DS, Jonathan would say in rehearsal, and then we kiss here, right, instead of actually rehearsing the kiss. Still that technique did not hurt, especially in his kissing scenes with Lara and some with KLS.
I would say that to me the hottest kisses on DS were the two passionate ones between Barnabas and Angelique in 1795, and most of the Bramwell/Catherine kisses in 1841PT.