So my experiences with vorepede have always fallen into 1 of 3 categories: It rots in my hand. It "dies" to oring, path to exile, faith's fetters, etc. Or it just steam rolls someone. You might say that those are pretty normal expectations for any large green creature, but I feel like vorapede does it in the least exciting way possible. However, I don't look specifically for cards that support pod, so maybe it does more in that context.
EDIT: As for the zombies, I used to do the whole gravecrawler thing, but I got rid of it eventually because of customs + I felt like bloodsoaked just played better. My thing against gravecrawler is that it can get downright ridiculous in certain situations (carrion feeder + mana or goblin bombardment + other zombie + mana). I don't have anything against aggro combo, but it felt like it occasionally led to too much of the uninteractive combo side. Bloodsoaked goes in the same deck, fills the same front end roll of a 2/1 B creature, but doesn't get quite as dumb when you "go off."
Bringing this train back around, bloodghast in a vacuum is probably stronger and requires less pieces to be good. Relentless dead with a small number of zombies is interesting to me because it can already get value with no zombies, and its a decent beater. Relentless dead with a lot of zombies seems kinda gross, but I think this reaction stems more from my feelings towards gravecrawler wombo combo. So pick whatever road appeals to you.