which servant is worth for me to saving?

What?
I'm assuming you're asking of a good Saber, Archer, and Berserker. If so, here are a few suggestions:
Saber - Lancelot (Saber), Okita Souji, Altria Pendragon (Alter)
Archer - Gilgamesh, Oda Nobunaga, Tristan
Berserker - Heracles, Minamoto-no-Raikou, Cu Chulainn (Alter), Ibaraki-Douji
You may notice that all of them are 4* and higher. Well, since you're saving up, you will be using quartz, right? 4* and above have stats generally higher than lower-rarity Servants.
Also, it's no question that the one you should be saving for, if you're not confident in your luck, is Merlin this December.