Thanks to all of you for your answers, I finally choose to buy Saki, for her utility from time to time, and because "more waifu more laifu" And, a little more seriously, cause I still need one orb and CCing my fooders for Spica, leaving me a little bit of time.
Thanks again for helping little nooby me, and have fun on Aigis ! (now back on farming Rita, or at least trying to drop her XD)