As the main character of Fate/GO, Mashu is the first servant that everyone obtains at the start of the game. Even though she lacks any kind of offensive abilities and her damage output isn't that great, one should never neglect her as her true potential will be unlocked after progressing through the storyline. Besides the usefulness of all her skills, the materials needed to upgrade them are also much cheaper than the other servants. Moreover, by having a team cost of zero enables her to fit inside any party especially if you have problem with team cost at the early stages of the game.
Among all the 3* servants, Cu's survivability is acknowledged to be second to none. With a three hits self evasion skill that has a short cooldown of five turns at max level coupled with self guts and debuff removal, Cu has everything that he needs to survive tough battle while poking down the enemy's health with his lance. Furthermore, Cu's NP also has a certain chance of killing the enemy instantly which you can try again and again even if you failed, thanks to his high survivability.
Put your faith in the light as Saint George is a servant that you won't regret raising. With a skillset that is meant to tank damage for the party and having up to 9200 HP as a 2* servant, George's main purpose is to ensure your squishy members survived until the boss stage and not get accidentally taken out in the early stages. Even though his high star absorption might be a slight disadvantage as he would compete for stars with the main attackers, but by that time he should be quite dead so he won't be getting in the way anymore x) Skill level order: 1>2>3
Arash or more commonly known as STELLAAAA is considered as the best 1* servant in the game due to his insanely high NP damage for that also kills himself in the process. The only use of Arash in battle is to build up his gauge either by equiping a kaleidoscope CE or obtaining NP charges from his party members and then unleash his devastating NP onto all the enemies and dies, which sounds pretty tragic for him. As Arash's skills also do have any effects on increasing his NP damage except by providing some NP charges, he is one of the cheapest servants to raise without needing to invest much on him for high damage.
Robin Hood as an insanely high damage NP for a 3* servant, not to mention that it is easy for him to reach NP5 due to being a 3*. By ultilizing the NP gain from his second skill and fit him inside an Arts party, it is possible for him to use his NP two to three times before he falls. He also has quite a high HP as an Archer class servant and has an one turn self evasion skill to protect him. Another benefit of Robin Hood is that his skills do not have any increase damage effect on his NP so it is possible to save on materials to level them.
Does not have Waver? Doesn't matt... well it does matter for quite a bit. Andersen is kind of like an apprentice of Waver, providing critical damage increase and critical stars to the party with his first and third skill. Besides that, his NP provides HP recovery, attack and defense buffs to the whole party but do take note that it has a certain rate to succeed. Another weakness of Andersen is that he might get taken out accidentally due to his low HP. Therefore, it is still better to get a Waver support but Andersen still has his own use as a budget support.
By having three skills that can boost the party's damage and a NP that deals considerate amount of damage to a single enemy, Caesar is an excellent servant to have especially if you do not draw into any high stars Sabers. Even though he isn't the type that you want for husbando material, he can get the job done without much problem, if you aren't sceptical with his looks that is.
As the gap between the damage of a 2* and a 5* is too much to be covered, don't expect him to do as much damage as the other servants. However, Hassan has the best critical stars gain among the 2* servants pool and the chance to insta-kill an enemy with his NP ranks him much higher in the list compared to the others. Remember to use his self-evasion skill as frequently as possible to ensure his survival.