Observationally, how can one decide which of the four general expansion models best describes the present-day universe?

Answer: Recollapsing-no dark energy and matter density of universe is greater than critical density (Big Crunch-BB). Critical - no dark energy and matter density equals the critical density (not collapse but expand slowly). Coasting - no dark energy and matter density is smaller than critical density (universe expands forever w / little change in rate expansion). Accelerating - dark energy exerts a repulsive force that cause expansion of the universe to accelerate with time (more dark universe). We can tell the lookback time to the supernova from the distance and how much the universe has expanded since the supernova explosion from their redshifts (tells how fast universe expanded).