Never understood why would people not play lod

Chaos runs have more involvement and actual gameplay compared to sitting in a small room while Baal spawns monsters

It's like playing open bnet, retardedly over stated items, except you have to pay money for them. NOPE f that shit

When paladins are teleporting you know it's a joke

And overpowered merc? Dont even have to do anything while merc solos game. Nahh

No skill pay to play, I'll pass on expac

I don't think the question here is "what's hardest" if you look at the topic title.....

Here is a list of few different stuff I know abou classic

Stash is smaller
Monsters give less experience
As relm said, static is buffed (no lifecap)
Some builds become useless because no mercenaries equipment (javazon, light sorc)
Mercenaries and skeletons from summoner dies upon act switching
You don't require level 60 to finish hell baal.
Whirlwind is overpowered, hits every frame, even if low attack speed
No runes, rendering a lot of builds useless
No act 5
No assassins and no druids
No exceptionnal and elite uniques (only exceptionnal rares)
No elites at all (white magic rare set and unique)
Limited access to set items
This all means builds are often much stronger with rare items.
Bowzon is completely obsolete, same goes for a zealer.

Well Java and Light Sorc are not "useless" at all. Bowzon & Zealer are obsolete? For Hell CS, yes.
And the question "what's hardest" is one of the differences of classic and lod. ;)

I cannot say since the dawn of time I have yet to install xpac(even to get the higher resolution)

Purist