this file is inside your data-folder or grf: data/clientinfo.xml
(since you're using eAthena: if you're using a old sak-exe it's the sclientinfo.xml, you'll find it on same location ^^)
I'd prefer an sql-table since configuration and administration (maybe using a webtool) is easier this way...
(my oppinion since i'm scripting nearly everything with sql-support to configure it via my cp.. xD)