continuum might be the most recent but it also violates op request on pack style it is not a big pack it is an attempt at a hardmode pack(be ready to do bees if u truly wanna play it,people say ignoring them degrades the experience alot)I don't do public servers, but both FTB Infinity Evolved and FTB Continuum are more recent additions to the 'official pack' list. Continuum is the most recent, and most likely to have a higher number of active players.
The most recent ftb pack thats mostly just a big pack is ftb beyond.
On the 3rd party packs side yes atm3 is a nice one and it has a truly endgame goal (one thing @Citron does not mention is there going to be a major update soon, check the atm3 reddit for details)
Another note-able pack is Enigmatica 2 https://minecraft.curseforge.com/projects/enigmatica2 it even has a guide in the shape of a questbook