Should I buy an I phone, if so, what model?

I am a thirteen year old girl and I have a fault but still working Nokia Lumia 520. I have been saving up for ages and I have over £400 All my friends have i phones and they always i message and do stuff that I cant on my phone. I was thinking of getting a second hand I phone 5s but I don't know if it is worth it. Any opinions would be nice thanx

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