I’ve been out of the game for about a year and a half and I know nothing of the new expansions. Which of the last 3 expansions are the best packs to buy? I already own all of classic and most the important cards that will be rotating out next year.
Hearthstone Mathematics does really good analyses of this question, they did one for Rise of Shadows and one for Saviors of Uldum. Unfortunately, they haven't analysed the data from Descent of Dragons yet, but the Uldum video would still have some useful info:
At the time, they said that Saviors Packs were nearly twice as likely to give you cards that you would use in the meta as Rise of Shadows. But when RoS came out, it was by far the most influential set (although that was partially because the entire Year of the Raven had weak expansions and everything else had just rotated out).
There are still a lot of Uldum cards in the meta -- one thing I have noticed about Descent of Dragons is that the epic cards are a little weaker/less represented, which makes it an easier set to craft from.
Could try HSReplay to look at the data directly -- or think about which class is your favourite and target the expansion that had the best legendaries for that class?
Another thing to keep in mind is that there is a nerf that's still live right now. If you buy any packs from this year, there's a chance at getting a nerfed card which you can disenchant immediately for full dust. The four cards are:
Sludge Slurper (RoS), Mogu Fleshshaper (SoU), Corrupt Elementalist (DoD), and Faceless Corruptor (DoD)
All of those are rares, so there's a good chance of hitting some of them, whichever set you choose.
if u only intend to play standard i would suggest on skipping whichwood, boomsday, rastakhan's rumble; as these 3 will be rotating out in around 4 months from now. Thats alot of time but still I would suggest catching up on uldum and descent of dragon. Rise of shadows has some good stuff too but uldum is really important with all its highlander synergies and so is DoD.
I recently came back myself, albeit im a wild player myself so what i did was to first buy packs of each expansion i missed to get the early 10-pack legendary (averaged around 4-6 packs each expansion so took abt 25-30 packs in total) . once i had that out of that way, I just checked packs which synergize best with wild meta, which for me which for me was mainly uldum.
I would personally recommend you get the 10 pack legendary out of the way and start with DoD and uldum.