My gelding is in a French link eggbutt snaffle. The link doesn't lie flat against his tongue - in actual fact the edge is against his tongue, sitting like a Dr Bristol "should" [it is a french link though, it's just the way it sits in his mouth] - but he prefers it over an oval link for some reason, salivates better and responds more quickly off a lighter aid.
My filly is in a D ring snaffle. Single broken. She doesn't like double jointed bits for some reason, and I'm not a fan of full cheek snaffles because of the safety risks [and forget keepers, she likes to be able to dictate the angle the bit sits at]. I won't use a loose ring on a breaker. The D-ring seems to be the best option. She has a sweet iron D, and a stainless steel D, and while she's still a breaker not just a greenie, she's going nicely in both, though she seems to respond better to the sweet iron.