95% of season 18 private servers are IGCN based, the rest might be xteam or mudevs, xteam as @moaacir said, i agree totally to all he said, what i like from xteam is = season 2 files for example, cus they have good re-worked features and so on, but for last season nah, igcn is the king of the configs, progression, community,support, tools server and client side as well, more professional service, better structure of config files than any other server files if u use notepad c++ its all simple to understand.
now what difference could be is 1 thing, mudevs server run abit faster when u start .exe files, and maybe have less programs to open, so it feels like 'light files' igcn on the other hand need good ram atleast min 12gb ram and even 8gb but better 12 nowdays for s18. and mudevs seems like xteam for me, i dont like the new structure of their config files, the eventbags and all that, its more complex, its like they tried to do like igcn .xml but its more messy for me to learn, and i dont think they have good file editors for configs like igcn does, but at igcn files even without editor u can config easier than mudevs or xteam, i dont understand why ppl re-make files and dont properly make a normal config file with organised order of each config and a simple explanation what is what, igcn has all that which is professional and worth it and they have great community and bug report system and discord and extra plugins and tools etc that u can get, most importantly i hear the offattack/offtrade plugin u must buy for ur server, then a launcher premium ffor ur auto updates and some client protection, igc essential editor server side for accounts its included free and its the easiest account editor ever. Client editor there is lite version of toolkit free for limited edit features, but the premium one is a lifesaver which is only one time payment product and u can view almost everything as image,models etc in client, and if u wanna go advanced u can reconvert with extra plugin u can get as an addon too for toolkit, so at the end if it has everything u need and u are serious for opening a serious server with ready investment then that is my view, igcn, maybe later in some years if the other dev teams update and do something more professional they could be worth to use, mudevs has free season 17 files which is nice, ofc including bugs or issues, igcn dont have that much free files for latest seasons, probably max = s6 then s9 and s12 which are gr8 files too, but u know s6 most ppl go for louis s6ep3, s9 = igcn nice, s12 = igcn, and for higher seasons u must decide what u care about and pick what suits you better cus there are people who are fine with just buying files and open a server and ignore issues and bugs and just make a server, while others know how to operate a server and care about features to be working and having a solid way of working with the configs and managing the server.