Well, I disagree. With agri viral you have to get your planets one by one(you can`t build agri infra on infected clusters), unless you kill a viral which is highly unlikely(not impossible though). Tax viral makes a lot, especially when the food is around ten and lower(even when food is 15 it makes a lot). Considering the current state of RT tax viral will give you more pleasure in the short run but in the long run noone knows... You will make billions in a week, I can guarantee that. But the base PR could be a problem if you are not used to it(but you are :P)