From south beach it would be best to just drive the whole way.

From Biscayne or from Brickell if you are near either of the metrorail stations (govt center or brickell) or near a metromover stop(connects to metrorail) then i would take the train. On normal days the time savings wouldnt be huge but much less stressfull than driving on US1 at rush hr every day. And anytime there is an accident or other delay on US1 you will come out way ahead timewise.

Unless you are dead set on south beach or Biscayne i would take a look at Brickell. Plenty of new buildings a short walk from the Brickell metrorail station so would have easy commute to Dadeland as well as painless train service to MIA for two bucks.