What game have you played the most?

On Steam:

1. CS:GO - 1315h
2. Dota 2- 1004h
3. Planetside 2 - 919
4. Firefall - 676h
5. Warframe - 542h

Outside Steam(That I am aware of though probably spend at least 1k hour in several f2p MMOs... each):

1. Guild Wars 2 ~ 3200h
2. Mass Effect 3 - 365h
3. Mass Effect Andromeda - 270h

https://en.wikipedia.org/wiki/Starsiege:_Tribes

Even AAA games today have gradeschool netcode compared to Tribes. It plays fast and smooth even over a dial up with realistic physics for projectiles and players with good prediction to reduce observable lag. Of course it had custom maps with prefab buildings & objects, etc.

Even AAA games today have gradeschool mods compared to Tribes. It has not just vehicles and modifiable maps but even total conversions into persistent RPGs.

And Tribes 2?

It had all of that plus built in offsides balancing with bots that were replaced by real players when they joined out of the box.

(Tribes 1 & 2 were done by a team at Dynamix that came out of the Commodore 64 & Amiga scene. Tribes 3 & 4 were trash on different engines coded by PC people that lacked almost every quality that made Tribes 1 & 2 special and had much worse net code. 3 even has worse graphics than 2 and 4 aka Ascension coded decades later barely matches Tribes 2 in graphics and doesn't include the netcode, physics, bots or mods.)

TF2 with a whopping 9545 hours,not sure how many of those are idled,but it's still a doozy.

propably Civilization II, i'll never reach hours spent in there :)

Anarchy Online...

Couple hundred days maybe dunno...

Ekarona has played 358 days 9 hours 18 minutes 6 seconds
Ekaros has played 27 days 20 hours 7 minutes 16 seconds
Ekaslave has played 344 days 14 hours 25 minutes 56 seconds
Ekadv has played 10 days 23 hours 39 minutes 2 seconds
Ekax has played 6 days 0 hours 3 minutes 36 seconds

Hmm maybe around 18000 hours or so...

No idea how much time I spent in it, but probably Ultima Online.

The Witcher 3.

Insurgency with CS:GO close in second place.

Victoria Revolutions - only game I played for ten years, literally an hour or two every day.