Bridget nailed it. It’s really about what you want to achieve.
Zeke is awesome in all sorts of applications, but isn’t the best value in a ranged offensive team. That doesn’t mean he’s unusable, just that he will draw all the fire from green and likely die quickly in a few raids.
I run a Mira team on offence, but Shiva is in there. That stun on round 2 is essential to my strategy. I’ve had to compensate for her not getting a leader buff, so her claws are HP Def and AP. People say she is useless without stun claws. That hasn’t been my experience at all. I have found her utility to be unmatched.
Tyreese is definitely worth it. When you can acquire him, don’t think, just do. He is one 6* I was apprehensive about getting, but when I did, I was very satisfied. He really does hit hard, and decapitate is great against revive teams.
I’m not sure about Siddiq as I haven’t used him. I’ve heard good things.
It sounds like you’re in fairly early/mid stages of the game, so I’ll recommend Zeke. The reason being that he has more all round utility. He will help you in things like SR and Fac Assault. I know they’re not as cool as war, but they’re more frequent and give decent rewards. The more rewards you get, the faster you’ll grow so it would be an investment.
If you go with Ezekiel, you’ll need to start thinking about his weapon. He needs something built specifically for him. I would suggest starting with a kukri. Add either Abs Def or bonus Crit to slot 3. Then either upgrade slot 1/2 and/or add AP to slot 2.