For me, it really depends on the matchup. If it's against Fox or Falco, I'll go for back air stage spikes or capes on their recovery. If it's against a character with a predictable recovery like Captain Falcon or Ganondorf, I'll use Megavitamins to gimp their recovery. If it's against a character with a versatile recovery, I'll wait onstage and barrage them with Megavitamins, and then hit them with a smash attack when they're vulnerable.
Generally, though, I always use Megavitamins and smash attacks when edgeguarding, often times not even opting to attempt an offstage edgeguard. With Dr. Mario, it's risky to try offstage edgeguarding, since if you get hit, it can be difficult to recover. Heck, if you run off the ledge with a forward air, you can just barely recover from that...