Do it in Lava.......
but make the Lava substructure all the way down to the tissue, and make the lingual in Lava as well for strength. This will allow you the room to go deeper in the embrasure areas and give that 3d effect that so many need. In addition, the last thing, is when it comes to the way the pontic adapts to the tissue. Relieve the model a little bit, that way in the mouth, the pontic blanches the tissue very slightly, so it actually looks like it's coming out of the gums. Now some folks here can explain how you can use external/internal stains to give you that 3d effect and out of the tissue effect as well.