Warframe for me. The only advantage D2 has over Warframe IMO is the high production value(mostly graphics). Outside of that, Destiny not only is more expensive, it has a LOT LESS content. The grind in Destiny is worse than the grind in Warframe. And the rewards in Warframe are more meaningful.
So that's my personal opinion. Graphics alone wont make me buy D2, and that's all it has to offer... good graphics.
I am going to play devil's advocate here and say that companies love to justify microtransactions because "some people don't have much free time to catch up to everyone else". Following this logic i will say that not everyone has much free time to subscribe for long enough so now its easier for them to get their vet rewards.
NOTE: At least SE is nice enough to give vet rewards. Other companies would rather sell those items to you.
i think that question is really more based on personal experience and preference. For example, no matter how vast and beautiful a game world is, if it lacks rich story, lore and life-like npc behavior that is involved in the world itself and its story, then the game is not enthralling or immersive to me.
Its gotta have a combination of those things. And of course other factors, but to me those are the more important. Also interaction with the environment and many quality of life details in game are important too. An empty world or one that you cannot interact with can be really just boring.
To me personally, Tamriel(ESO), Azeroth(Warcraft), and Tyria(Guild Wars) are the most immersive because of the combination of those things i mentioned. That´s really why i play those games and love them.
Many mmos have one or the other things i mentioned and lack the rest, and that hurts the immersion. How can i feel immersed in a game world where all npcs are lifeless statues? or the story is just an afterthought but you never know what is happening in that world because the main activity is just mindless grind for levels even though the world is beautiful. That is really a shame.