In my opinion, it's Mini-missions. However the server has lost it's popularity now.
It was the 1st multi gamemode in Mta with tdm,tdmnp,dm,dmr,race,ctc,ctv,vdm and few more gamemodes in it. It was created by R3mp, Djlobo and Stuart in 2009. I remember server was always full back then but few days when i visited the server i saw only 30-40 players.
Gamemode wise i would say mini-missions because it's unique but it's not popular now.