Practically the same ones every day and not enough of them at that. People are glitching their way to rank 3 which IMO is fair game since they haven't patched it and it takes bloody forever to rank up legit even with the Nightfall buff when you only have 4 (possibly 5 if you're the right class *ahem Hunter*).
Or at least give more ways to earn rank such as doing Hive related Heroic story missions, completing parts of the raid, or ROC strike for Summoning Pits or Will of Crota. I'm just spit balling here, if anyone else has any ideas they could implement please feel free to share.
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It's designed this way to keep people playing, instead of giving a reasonable amount of content to keep people busy they just intentionally bottle neck progression.