This might help you 'mal.
[
pad.wikia.com]
http://pad.wikia.com/wiki/New_Players%27_GuideNinjas suck, and elemental resist dragons suck.
Awesome monsters are...
Neptune: His action skill is fucking amazing since it ignores defense. Poison lasts until the enemy dies. At max level and max evolution, he can deal 7,000 damage which is amazing against high defense enemies.
Orochi: Best survival skill in the game. Delays every enemy's attack by 5 turns. Also his leader kill lets you survive any hit as long as you have at least 50% of your HP. With proper setup and low HP you can heal yourself to over 50% each turn for constant survival.
Shiva: Destroys 100% of all enemy's defense for 1 turn. See Neptune for why this is good.
Amaterasu: Amazing healer (probably the best) when set as a leader or helper though it takes a long time to make her good. Until then she's not as useful as the Siren. If you have her, everyone will want to friend you.
Tsukiyomi / Venus: Their active skill lets you move orbs freely for 10 seconds without activating any matches till the turn ends. Which can let you make a godly combo.
Isis / Horus: Damage multiplier when you manage to use multiple elemental attacks in one hit. Isis is 3x for 3 different elements, Horus is 4x for 4 different elements. Hard for beginners though since combos take some practice to get used to. Also they requires you to have different elemental monsters in your team, which means no mono-color teams. Isis's active skill is sorta meh though.
Lucifer: Mediocre attack but fucktons of health and recovery which is amplified by his leader skill which doubles the health and recovery of every dark monster in your team. Also his active skill deals a fuckton of damage.
Ancient Dragon Knight: His previous forms drop from dungeons, but if you roll him in his max evolution form, then he can be useful if you use Dragons.
Also useful are mono-color-team monsters like Ares, Peresphone, Loki, Pavarti, etc.
There's also Odin and Deity Odin but you can only get them from the Egg machine during Godfests and I dunno when the next one is gonna be.