Samanusoke
The best out of all of them, this guy is a beast. I rune him for assassin-ish spec: HP, attack damage, physical penetration, and a sprinkle of armor and lifesteal. I have tried him full tank and he is beastly but lacks killing power. With this rune combo, he is high DPS and once fed he is VERY tanky. My preferred equipment set is: Resist Boots, Sharp Spear, Wintry Feather, Crystal, Force of Gods, Ferocity.
Combo is to enter combat in dual wield and use skill 1 to close, then skill 3 to slow and 4 to switch stance. Then use skill 3 to force back and stun, followed by skill 2. After that either skill one or melee until you can use 4 to switch back, then stun, slow, and close. Very quick to start, very strong to finish. Can cross the map so fast, perfect for closing up lanes.
Definitely S Tier.
If your considering buying a new hero, buy this one. Or dont, and I will kill you with him
Monica
Fun to play for sure! I have her runed as a mage, ability power, magic penetration, and lifesteal. I use the default nuke equipment set. She needs to jungle until she has 4 abilities, and after that she can "one shot" most non tanks simply by casting 1,2,3,4 right in a row- its a lot of damage. Later in the game, she is great to hang back and dodge, then dart in for the kill with her ultimate. She is a little bit squishy at times, and there are certain classes I have a very hard time killing with her. Worth purchasing her to have fun, but I do not consider her to be S Tier.
Ymir
Wow, what an OP mage. I have him runes pure ability power and magic penetration, with as much health on top as I could get. For equipment, I use: Piercing Boots, Lament, Lament, Scepter of Life, Magic Cluster, Magic Cluster. The trick here is to output all of your DPS at once: 1,2,4 all onto one person. Almost no one can withstand that much dps on top of the stun, including tanks. The downside to this guy is his slow movement and lack of "running away" power, though his shield is nice to block some damage. Coupled with some defensive shields and you can use it to get away if needed. If you like range/mage classes, this guy is a good pickup. I have not played much since the nerf, but I assume he is still a killing machine, just slower at it. Borderline S Tier.
Olivia
Wow, a complete wiff here. I have tried her full on DPS. I have stacked health. I have gone full tank gear and runes- no matter what, she just doesnt cut it. She does not have the ability to stay in the fight like Bandina, and she doesnt have the tankability of Samanusoke. She is a glass cannon, but not even a better powerful one. When I come against Olivia in play, I have no problem ripping her up with any class... and then I play her, I get wreaked. Sure I can have a good game and get fed early and ine shot with her ultimate, but more often than not someone looks at her and she is dead.
In my opinion, the worst out of this list.
Hippolyta
The newwest hero, I was very excited to try her. And now that I own her, I wish I had my money back! She is an EXCELLENT support, and her ultimate is soooo overpowered. But outside of that she is lackluster. She is a little tanky, and has no abilities to move fast or escape. Her ult is high cooldown, so once you use it your basically useless for the cooldown.
Her second skill is powerful, but here are the problems. With the charge up, it makes aiming tough. I understand that's part of playing her, but if in the 2 seconds between you releasing the button and it landing, ANYTHING happens, the skills fails. I mean, if you get frozen, or stunned, or the enemy moves at all- you don't get the hit. I have died mid air many times, and been stun/frozen mid air many times as well. IMO they need to make her immune to CC while in the air with the hammer stun.
My strategy for her is to use skill 2 to jump BEHIND enemy lines/group, then use skill 4 to stun them back towards your group, or into tower range, etc.
I rune her for tank (tried assassin eq and runes and she sucked even worse) and she is ok. In group melee, she is a goddess- her ultimate stunning 5 people while your team rains down hellfire is serious power... but thats it. Second worst character out of new ones. Dont buy her unless you got extra gems, wait till she is attainable with gold, etc. Definitely not S Tier.
All of these notes are my own opinions. If your #1 player in ranked using Olivia, more power to you.