It is worth the wait. I spend the first couple tandas just looking around the room to see who is there and where my favorite partners are seated. Then when I'm ready to dance, I'll try to get the attention of someone. Everyone dances in a close embrace in the milongas because the floors are crowded and this is how tango has been done for so many years in BsAs. The only exception I have seen is on Saturday night when couples may dance salon style in certain milongas where there is more room to dance.
Men dance with certain women on a regular basis.
They may have a particular woman with whom they enjoy dancing milonga traspie or a certain orchestra. It takes time to be known in the milongas and to be asked to dance by the best dancers. It's only going to happen if you are here for a long time and get to be known. They have been going to the milonga for years and are given the same table every week. If you are going with two or three friends, it is advisable to call and make a reservation around 8pm.