A very important part: if you are thinking of the Holy Grail War system of FSN, there's an order in which the servants are summoned: from the weakest to the strongest. Remember when shiro summoned Artoria when Lancer is chasing him? That's why. Saber is the strongest while Zerkers are the weakest. Illyasviel actually spend 3 years before the war to train her skills with Heracles and endured various hardship in the process. (I think this is revealed in FHA). So, you are coming home, and you see a Zerker on your couch... Your first reaction should be: "crap, where is the rest of my room? why is there so many debris? whose blood is this?...." Of course, Zerker could also be Kiyo or cat or some other ones who actually talk, in which case... you better elope to some far away places because you don't stand a chance of winning the war with them WWWWWWWW

As for the dislike servant, I guess it would be Spartacus, with or without the Zerker limitation. I actually like the historical figure very much, but his FGO image, personality, and, especially, that creepy smile are all unbearable. I will either kill myself or kill him before my brain blows...