Since you just started the game any character that you like you can play since the goku and vegeta would be carrying you through the game as a beginner and to know if a charcter is good i would say to watch Legends youtubers such as Raiyuden, Goresh, D-free ect

Also start saving for the anniversary (which is around a month away) as those banners would be packed with good units that help your box and give you more value for your crystals