Throws are no longer weight-based in this game, so Dthrow is consistent on every character thankfully (as far as end lag goes).
Dthrow at low percents unless near ledge (to instead quickly Fthrow or Bthrow) and follow DI for a jump Uair or Bair, then feel out the situation — but you generally want to land before them. Watch out to not let the game give you a short hop aerial (don't input jump and attack at the same time, which sucks because working around this makes the tipper harder and inconsistent).
At slightly higher percents, you almost always should Fthrow and Bthrow (whatever is closest to off stage). Fast fallers can be Fthrow'ed at low percent and caught when coming back down with a Ftilt or Fair (run as far as possible, don't jump too early), and pray that you'll catch their double jump. Also at low-percent, Bthrow can lead to a tech-chase. It has less end lag in this game.
Uthrow sucks as a kill move. If you had to use it, you failed at this stock. This reality is sad, as it makes Lucina a much more viable option. In Smash 4, it hardly mattered when Marth couldn't kill because he could just Uthrow. Melee and Brawl's "Marth syndrome" is back.
Pummel as much as you can in this game. Successive pummels unstale your other moves now.