My $.019-
All three have flaws. IMO- GD is no more or less flawed than HD, but the community is much more resistent to change in GD for whatever reason. (A guy abandoned his GD team in my conference... two seasons later they are still ranked... and people claim talent doesn't win games!)
HD feels like it has less downtime than GD, due to shorter recruiting, shorter playoffs, and more regular season games. There are some flaws that you'll find, and usually they are nerfed/fixed relatively quickly. The major gripes right now are around recruit generation at the low-DI level.
HBD makes GD and HD look like side projects- it's incredibly more involved, as you manage 5 teams, not just one. Along with rule 5 drafts, injuries, promotion and demotions- it's great fun, but I equate the effort for one HBD franchise to 3 or 4 HD teams.
GD bothers me because I don't get it, but I do feel like vs. HD there's a lot less to do in GD, as if you don't have the talent, no gameplan will win a game for you.