How do you actually level?

I both rush/power level and do some hell runs, but mostly i play alone, so i farm all the bosses over and over.

I do 1, 2, and 3 depending on my choice of build. I push on through nightmare to run nightmare TZs to farm for loot to buy an anni and or Torch or both and other items. Then I finish Hell.

I never do 1, I never use the predetermined "the best leveling build" and then respec. I do respec 1-2 times per character during a game (before lvl range 85-90) but I tend to 'save' as many free respecs as I possibly can, even tho some stats can be tweaked even in those later/end game.

For the actual leveling and going thru the game... Well it depends on the mood/time I want to spend on a particular build, character or just in general at that point on D2R. However, I do mostly either solo, walking and killing everything thru the game or I join lobbies with many random people and while they are doing their things I level up on players many on my own. I rarely go for the "full rush" as in all difficulties in quick sequence, even if I get rushed, for example, thru Normal then I'll play/farm alone for a bit on Normal and Nightmare and eventually may again take a rush on part of Hell (but that usually takes weeks).

About gear part, whenever I make a new character I usually just put some of the BiS items to sit in their own personal stash and then put some decent 'leveling gear' as well for the road. But I often, at some lvl thresholds (like lvl 18/27/30/50/67/70/75) go out and just swap out that "leveling gear" for something else if I feel underpowered. Or just simply craft/save something along the way if I find resources for that.

P.S. I almost never do "runs" in general or farm deliberately for items or runes. The only thing I do from time to time is go into cows with some top char and try to find bases or just have fun with low(er) lvl players and such.

I genuinely love the playthrough experience, so I'm a bit odd when it comes to this. I'm mostly option A, but honestly, I don't always get to the respec phase. Sometimes I just beat Hell

Baal with whatever wacky leveling build and then delete the character to make room for more playthroughs.

BTW, Bliz, I need more character slots.

Mostly A, but the respec is usually more to adjust stats after Anni and Torch are on (hey, useless strength, turn into life please !)

I prefer gathering some lowbie gear and play naturally through the game, but I won't decline a rush if someone offers.

I voted for the second option because I go for the best build allocation points even if that it's not optimum early on.
And later on, as Necrarch said, I respec for points reallocation after Torch and Anni, not for changing spells.

kill everything in norm/NM, then join hell cows till 70-80

I enjoy playing through, so if the build available to reach final status without respec, I play that way. Otherwise, after reaching certain level I respec into final build.

For me it's a combination. I do really enjoy playing through the game for the most part. Just toss some Sigons onto someone and join or make a game for whatever Act you're on. Fun times. Sometimes I do feel the need to be rushed, which usually happens by accident. I'll make a game like "Act 1 Begin" and someone will push me all the way through to A3-5. I always try to pay, if they accept. I'd say most of the game is still very enjoyable, minus parts of A3. Respec is something I'll do only if I managed to mess up the build I was going for, or looking to change it up later.

I solo a lot since I play on Switch and finding games can be difficult at times, so I do a mix of 1 and 2. I need to deal with immunes so I kinda hybrid when about to enter Hell, and eventually I Respec to full synergy build. I do usually Respec once entering Hell for the vitality points even if I still stay hybrid without gear to go all in with yet.

Javzon was poison hybrid until Thunderstrokes

Immolation zon has stayed hybrid with Mist and

Strafe

Fendzon just needed Decrep and sunder but she used

Charged Strike a lot until then

Rabies/summon Druid probably will keep the same

I start with the desired build. Sure, if it uses a high level skill (such as FoH), it's tough, but you can leech through the early levels online. I started playing when there were no respecs and it was never an issue for me. And since they're limited (during levelling), I hoard them "just in case they're really needed" (i.e. never).
FWIW, in Median XL respecs are free and unlimited until level 50, so you can truly try different builds there and choose the one which fits you.

Speaking of levelling itself, I join public games if available, and strongly prefer walks over rushes (although if someone offers one, I join it anyway). However, after the game ends, usually after completing an act or difficulty, I create a private game and go back to complete missed side quests and get all the waypoints. If the rush ends after Act V, I join Baalruns first, so my character is stronger before clearing the difficulty.

It's funny, this is quite a nuanced question. It depends on a lot of factors. The class in question, final build in mind and if the character can get items from other chars or if it's first build on new ladder.