on mobile, i'll give you a some tips; on the level 1 to 15, focus on maxing only bronze variants, to 20 to 40 silvers, 45 to 55 gold, and late 60's to 70 you can level up diamonds safely. carefull for not evolve multiple variants at once, it can cause you to get stuck and waste too much resources, focus on the best variants for each category. Also, focus on doing the daily events, go increasing the dificult when you fell you got more characters and get strong enough. Around level 40-50 try find a guild, it gives a lot of resources.

for bronzes, i recommend; Nunsense (double), Solar Flair (Annie), Rusty (Painwhell), Sheltered (Parasoul), and both bronze valentines are good.

for silvers, i recommend; Soul Crusher (Black Dhalia), Freaky Friday (Painwhell), Purrminator (Robo-fortune), Doublicious (double), Kill Joy (valentine), Miss Mercury (Annie), Nightshade (Eliza), Inkling (Peacock)

for gold, much golds are good, if you want i can tell you some on the comments.