I am a Marcus Smart fan. I like him, want him on the team. See him helping the team in ways that don't show up in the box score. He has flaws too, like every player. I can see the need to consider trading one of Smart, White, or Brogdon, we don't need to commit that much to the combo guard position, but I am not making the leap to "Smart needs to go".
Smart was great last regular season and down a bit this regular season. White was pretty bad statistically last regular season (although still contributed), but was very good this regular season. Brogdon was 6th man of the year this regular season. I feel that based on overall body of work, Smart is the most valuable of these 3. Not by a wide margin, all of them are good players, all relatively equal.
I felt that Smart was the best in the playoffs of the 3. I took a look at the stats excluding the MIA series, I excluded that as Brogdon was injured so it would kind of pollute and comparison:
Smart 15.8 pts / 46.5 FG% / 36.3 3P% / 82.5 FT% / 4.2 Rebs / 5.1 Assts / 2.2 TO
White 12.8 pts / 50.0 FG% / 42.9 3P% / 95.2 FT% / 3.2 Rebs / 2.0 Assts / 0.9 TO
Brogdon 14.8 pts / 44.6 FG% / 43.5 3P% / 84.9 FT% / 4.1 Rebs / 3.6 Assts / 1.1 TO
I can't list every stat but Smart got to the line the most, Brogdon took the most shots. Smart played the most minutes, although all roughly the same. (Note, in MIA series, White and Smart stayed pretty similar, Brogdon dropped off a cliff).
For defense, although White is a very good defender, Smart is the best defender and the most versatile defender. He can defend a wider range of players. I think this applies to these 13 playoff games and also in general. Brogdon is an OK defender. This is purely subjective, based on my own perception.
As to who should be traded, I would be fine to trade any of them, so long as we got back good value. Trade Smart and I am comfortable starting White (plus another big). Trade Brogdon, and I am comfortable with White as the 6th man. Trade White, and I am fine with Smart as the starting PG and starting another big.
If I had to pick though, for example a team said we will give you XXX young starting level PF, and you can give us any of these 3, I would offer Brogdon first, White second, and Smart last.