Which is the game you've played more hours ?

Steam:
Terraria - 727 hours.
FFXIV - 531 hours.
AC: Odyssey - 256 hours.

Origin:
DAI - 385 hours.
Sims 4 - 747 hours.

Honorable mentions: CTR, FFVIII, FFIX on Playstation. Super Mario Kart, Super Mario World, and Zelda: A Link to the Past on SNES. Oh. And WoW and D3 have an awful amount of time too, though I recently dropped Blizz games from my list.

Highest listed on Steam on my main account is 3DMark with 86 hours. Though I'm sure that's mostly idling. The family account has IIRC hundreds of hours in some LEGO games, not all of them idle, but a lot of that is my kids and their friends.

The game I played most was City of Heroes, around 1000 hours, I think.

Civ 2 MGE

1000+ hours I think :)

kf2 1450, maybe 400 idling

Ultima Online ...

Killing Floor: 400+ hours
Special mention: FF7 in PS1, the timer stuck at 99:59.99 so can't really count after that. :D

It would depend on the console, handheld or any other gaming platform or service on which I've played and how accurately time is logged as actual play.

On Steam, Monolith has me logged at 99 hours as my longest played game, which doesn't doesn't correctly account for afk pauses.

Steam 259h TW3;

Before Steam Oblivion 500h;

Gothic 1-3 2k h or more;
If we add Risen 1 and 155h of ELEX then I can surpass 2000h.

DS 1 and 3 now I have on steam 250h ;

Moe Mekuri SP, almost 350 hours in

After 5 days noone told you it's most* ?

CS: GO - 1632h.

Diablo 3 - roughly 1500 hours
All other games are not even close

FINAL FANTASY XIV Online
2,917 hrs on record

Dota 2
2,381 hrs on record

Path of Exile
1,247 hrs on record

Counter-Strike: Global Offensive
541 hrs on record

Steam
Stardew Valley - 206 hrs
Darkest Dungeon® - 160 hrs
Slay the Spire - 105 hrs

Non-Steam
League of Legends - 689 hrs
Minecraft - idk lol

Idle Champions of the Forgotten Realms - 17,333 hours. But it's an idle game and it runs 24x7...
Warframe is my most actively-played game - 7506 hours. But I've been playing that for yeeeeears.

Armello - 2, 313hrs (some of them are idle, the correct hours are somewhere around 2100, I guess)

Skyrim -- 900 hours on regular version, 99 hours on Special Edition. Eventually I'll play another hour to get it over 1,000.

The Long Dark -- 969 hours. Such a good game.

cs go but its mostly idle second would be warframe :D and then witcher 3

nothing much on a single game
but since steam had nba2k franchise i got 51+276+281+492+492+490+240=2322hrs

On steam: Terraria ~200 h
Outside of Steam: League of legends >1000 h, Call of Duty 2 idk, Pokemon Platinum >600 h

I have 8200 hours in Lord Of The Rings Online with my main character (what /played shows '11 months 1 week 3 days 16 hours 39 minutes 38 seconds', which is quite close to my actual playing time as I rarely idle). Other characters might sum up to half of that amount. I'd say it's about 12k hours in total (since I have another smaller account, characters deleted, etc.)

I have many games where I've spent around one thousand hours in them, but none in Steam: Quake, The Dark Heart Of Uukrul, Formula One Grand Prix, to name a few.

Eve online played almost everyday for almost 16 hours a day from 2009 till about 2014 kinda slowed down after that but also managed about 3k hours in skyrim and 2k hours in borderlands 2.

Csgo mybe 7k hours or more

Wolfenstein Enemy Territory, its not on Steam. When i was like 10-18yo i played it literally every day (my uncle showed it to me when i was small potato). No idea about hours.. thousands.. cca 8 years of playing? When i turned 20yo i somewhat lost interest in "gaming" and for me clearly if am rlly rlly bored or time from time with friends.
When i turned 24/25 or so i lost interest in moving images somewhat. 3 months nothing, then 3 days of lot of hours and then agin nothing, dont know cant enjoy it somewhat. Waiting on next stage :D
Like now, start GTA V.. doing 2 stunt races.. hmm quit. PUBG... 2/3 rounds.. hmm quit. BF V not even one round.. quit... lot of games like this. Maybe idk what to play, dont like story games, MMO/RPG taking too much time, i hate games where u must spend LOONG time to get playable stage... i like no brain shooters etc.. but its boring in while :D