Looking through the featured maps I would consider Otago, Obsidian, Isle of Grief, Iceland, Archers Valley and Shimmershore for teams MM. If the option existed to limit by team size I could come up with a few more.
EDIT: Shimmershore might not be deployed at present. Paradise Lost is probably the best small teams sea map among those I am sure are deployed.
Other options possibly better suited for 3v3-4v4 teams are Valles Marineris, some variant of Folsom Dam, FrostBiteV2 and AquariusCrossing.