Sadly the above methods of leveling are becoming a thing of the past
. Grushing is usually much faster and easier, as a new char to 70~ can be accomplished in a few hell chaos runs after being rushed. Some people are too lazy to grush in expansion so they grush in classic and then convert to expansion to skip finding someone to get the baal quest.
Another way is to get to act 5 hell and then leech experience in Uber Tristram, with the help of a hammerdin and a bonewall necro.
edit:
Myst said:
You may now follow the first guide's instructions from level 65 onward, with the following things to consider:
You can never enter the Worldstone keep in Normal or Nightmare.
You can never complete the ancients quests or have them be inadvertently completed for you.
Stop botting at level 97. Because you've exploited a loophole and had PATIENCE, level 97 for you = level 99. Go back and complete normal and nightmare ancients to immediately gain two free levels. This is the ONLY way to feasibly reach level 99 in one lifetime, and all of your level 97 and 98 friends will hate you
While this method CAN be done by begging for rushes and making "baal for quest" games, it is MUCH slower. If you have no friends, method#1 is reccommended for you.
More than anything, this method needs PATIENCE. You can't waste your ancients quests at 88 just because you're excited to get to level 90; just think about excited you'll be to get to 99 when you're only 97. By using ancients before level 97 you're wasting what could possibly be MONTHS of time and hard work getting those last two levels. Patience is a virtue.
That part is untrue, sadly. You DO NOT gain a full level after too long from norm/nm. After about 40 or so, you won't gain a full level from norm ancients, and after level 70 or so, you won't gain a full level at nightmare ancients. People still save these quests for 98, but they won't be getting a full level off of them. Instead them give about 1.4mill experience (roughly 14 runs getting both top 2 diablo and baal experience) each.