1x to get the original vanilla feel, any higher would just ruin the feeling and is mainly preffered by people who would want instant 60 anyways or servers who don't want to fix the stuff between 1-59 and rush xp rates so no-one notices their shortcomming, however kronos aims to fix everything without leaving out or hiding those bugs so there is no reason to rush the level since there is nothing that is intended to be hidden away. Those who really want the true blizzlike feel will lvl 1x at kronos, others could if they where desperate go to an instant lvl 60 server instead. :wink:
if you want a quality-filled experience of vanilla the best approach is 1x, the rate blizzard built the game around and for. :smile: