Who do i go to?

I have been in foster care for 4 years now, but my mum said that I can go back to her now! who should I go to?

whoever you feel would be best for you. At this point you can just choice who to live with based on who's your real mum. You have to choose wisley of who can provide you with the best future

There are points you need to consider. Are you happy with the way things are now? Why were you put into foster care in the first place, and is it resolved now? You need to think about what is best for your future. Maybe talk to your foster carers to see what they think.

If you know you are happy with what your life right now,stay but if your mom is telling you that she misses you,I prefer her because well she's family and you can only see her until you grow up. I hope you make the right choice.

Whoever you feel would be right to live with.
If you're happy living with your Foster parents then you can stay but, if things are okay with your mother, then you could live with her if she really misses you. You need to choose what's right for you.
I'd talk this over with your Foster parents and see what they say. Then if things are okay with your mother, then you can deal with that. You only have 1 mother and I'm sure she would like to see you if its been awhile. Think about this and choose what's right for your future.
You also have to think about who will provide for you and such. I wish you luck and you do what's right for you, not what others want for you.