I generally dislike the season-like mechanics and avoid them, but unfortunately blizzard has tied extra stash space to seasons in d3.
I do have the necromancer class and more-or-less like all the classes, but i really dislike restarting from zero.
Can you more experienced folks please advise what would be the best/easiest class for specifically reaching the requirements of extra stash in season 25?
I play this game solo so i cant lean on someone to carry me.
Thank you.
Next season, monk and demon hunter have two of the strongest sets as a reward for the seasonal journey. Barb comes next with the new Raekor if they buff it up a little bit. But you can easily achieve all seasonal rewards with any of the classes.
Necromancer and demon hunter have also the best leveling 1-70 process in my opinion. If you do the weekly challenge rift, using the materials that are rewarded to you, both classes have a 100% chance to obtain something useful. For demon hunters you want to upgrade daggers and for necromancers two handed scythes. Upgrade a lvl 70 yellow (rare) item using the third cube recipe, and the result will be a legendary item with a guaranteed affix of a damage multiplier that makes leveling up so much easier. You then cube this item and you will obtain its legendary power.
I wouldn’t worry too much about it. It’s very easy to complete the entirety of the seasonal journey with anything you like and decide to play. Season 26 has some of the easiest achievements so far.
There typically aren’t any major obstacles for solo players in seasons. Nearly all objectives in the journey can be completed during normal gameplay without much noticing them.
Propably the biggest hurdle in the season is the set dungeon. If you decide to play DH, I’d recommend doing the Marauder dungeon as it is super easy. Other classes also have easy dungeons.
The next thing is the conquests, to earn the stash tab you need to complete 2 of them. For S25 the 2 easiest are Divinity (GR75 solo) and The Thrill (GR45 solo no set items).
S25 will last a few weeks still so you’ll have plenty of time to earn the tab. 
if you play necro its the easiest set dungeons of all. but generally worst haedrig gifts (carnival and rathma is ok, everything else - waste of gift).
also, necro is the best startig class, since hes the fastest in reaching 70 and has good crafting chances at low level. check the guides on youtube or maxroll.
I was like that for years too, but I tell you, when I started playing in groups it was like a whole new game. You might want to give it a shot by finding a friendly clan. Just a suggestion, but if you want to stick to solo, I totally understand that as well.
Barb, because the IK set dungeon is the easyest of them all. And their Haedrig’s gift set is going to be the reworked Raekor which is going to be a strong starter.
Barb - IK (stunningly ez. I let my cat do it for me 
)
DH - Marauders (this season’s Haedrig’s gift 
)
I would go with DH. Marauders is the Haedrig’s gift. It has the most pop of DH sets (so easy to get solo GR75 and a TX rift in 2 min conquest) and it also has the easiest set dungeon for DH and one of the easiest set dungeons overall. There is no need to farm a second set which makes this super easy cheesy.
If you have any decent skill and take a little time to look up some 1-70 guides, you should be able to get your tab in well under 10 hours of play time solo.
Marauder can also potentially use Yang or Manticore which provides more options for gearing early on and Bomb Sack tends to drop more frequently than some of the other quivers.
As you’re only doing this for the stash tab, the fastest way is to ask for help in public chats. If you find someone to level you and carry you through a couple rifts at 70, you’ll save hours.
Probably the best start out with would be the DH. Maxsroll has a guide on what to do at the start of the season. Most important thing to do is the challenge rift during the kick off week on a new season.
Most of the replies here are for season 26, and he’s asking for Season 25, assuming that’s not a typo.
That said, if it’s for 25, Demon Hunter is going to be the fastest for the Shadow set.
But I’d probably level to 70 as a Necro, and once at 70, complete Haedrig’s Gift as a Necro, run ubers to get a HF Amulet & Ring, and then level a Demon Hunter. The Demon Hunter can be fast to level with Lord Greenstone’s Fan, but that is kind of skill heavy. Most players really can’t level fast with it, as it requires being fairly good at massacre bonuses, while running away from high level enemies, as you will be one shot. Tag & Run is a lot easier said than pulled off.
That’s the one great thing about Cursed Chest leveling. Grasps of Essence are an 86% chance drop, and Cursed Chests force you into Massacre Bonuses, so you don’t have to worry about breaking them. They typically focus on high end difficulty (i.e. much higher than you’d normally play), with quick bursts of 100-150 which grant as much experience as trying to do 400+ bonuses that take 10+ minutes apiece on lower levels, where you have to be very skillful to pull them off.
As far as Season 26, if you have the expansion pack, there’s no reason not to start Necro, and then switch over. If Season 26 is like the PTR, the drop rate of Petrified Screams is near 90% or so, regardless of the Greater Rift Level. Hit 70 as a Necro, run 3 Normal Rifts & 3 Greater Rifts. Start the Echoing Nightmare, grab the shield, and wait out the 1 minute. It takes roughly 2-3 Echoing Nightmares to level from 1-70. The Necromancer levels 15+ minutes faster than any other class, and the above is going to take roughly 15 minutes or so. So, why bother having one class at 70, when you can have two?
Now, as far as Season 25 conquests, GR75 and GR45 solo with no sets (that means no green items. Even 1 green item will fail this) will be the fastest 2 conquests to knock out of the way. And a DH Marauder’s set will be easy for the set dungeon. The majority of time will probably just be spent leveling up gems and running a couple bounty sets to get the necessary materials to extract 20 items.
As for Season 26, the 3 gems to 65 and the GR75 solo will be the easiest 2 conquests to knock out of the way. And Haedrig’s Gift is Marauders, making everything super fast. The majority of time will just be spent running the bounty sets for extracting items.
Season 26 I am thinking monk is the best as they get a powerful, albeit weakened, starter set and then necro Legacy of Dreams corpse explosion for filler/fun.
Might even start as necro to hit level 70 and then switch to monk for the paragon boost gained as necro, just to make it even easier.
https://d3.maxroll.gg/resources/conquests
here’s a pretty comprehensive guide for the s25 conquests
In a funny way this gives perspective to the discussion in this thread (about video vs written):
Like S26, S25 is dead to me. But demon hunter with the shadow set is a nice starter. Very easy to equip for except for a good quiver.
… gives meaning to the “dead” in DeadlyMouse.
I’d recommend starting monk get crudest boots and stick to speeds. keep it super-fast but go as high as you can. after you get plenty of screams make a marauder dh and farm them. you will have a massive head start if you can team up with friends to use your screams as a group, they will last 4x longer.
From the opening post…
I play the game solo too. that does not automatically mean I have no friends on diablo 3 though. (sometimes anyway)