This may sound like pretty obvious advice, but I would start by making a list of pros and cons for each option. Picking between Estonia and London can't be easy!
Think about absolutely everything that could come into play when making a decision, no matter how small or insignificant it might seem. It's always easier to make an informed decision when you have all of the options in front of you in black and white.
Once you have done this, you need to assess how important the things you've written are.
For example- London might have a much wider range of activities for you to do in your free time- gigs, theatre, culture etc, but the cost of living will be far higher.
If money is no object, then this may not be a big factor for you to consider, but if it is, then you factor this in, and also think about perhaps needing a part time job too, which could affect the time you have available to study.
Most of the factors will have knock on affects this like this, so you really need to consider the big picture when making important life decisions like this.
Good luck!