The spreadsheet already gives you the most scientific answer you'll get. Both options give you the exact same amount of AP, so the difference is crit vs. mana. If you aren't running low on mana (as would happen in short fights with lots of mana regen buffs available) then AGI would be better. If you find yourself running low on mana fairly often, then the INT card will lengthen the time before you have to resort to Viper, and it will result in more mana recovered over a set period of regen for those things that are based on a percentage of max mana.
You'd have to evaluate which situations you actually find yourself in to get the answer, although it's worth considering your other slots as well. By that I mean if you get 90 INT on your trinket, then you can perhaps use leather items in certain slots without worrying about lowering your mana pool. But if you aren't in the market for leather items, that wouldn't really be much of a factor.