You make your choice based on what you need, but in general, you should choose a regulated broker with decent customer support, preferably offering MT4/MT5. Don't fall for high leverage and some fancy promotions you might run into here and there, they all come with a catch.
Just go on and read reviews, and check some listing sites as well while you're at it, just make sure they are regulated for assurance.
If you look for FX brokers it's best to try FCA or ASIC like IB, HFM or Global Prime others are much less reliable.
Always check for their transparency in their rules, fees, and opt for a platform that's user-friendly with tools that suit your trading needs! I am satisfied with mine.
FCA brokers are mostly transparent since they are forced to reveal important aspects of their interaction with a client including order execution, withdrawals, controversial situations. Everything is set forth in the ToS. Not sure that offshore brokers without proper regulation adhere to what they write in their client agreement.
The most important factors to consider are how long they have been in the market and whether your money is safe with them. Beyond that, it depends on your strategy and preferences.
When choosing a broker, it was important for me that it had been working in this market for a long time, provided favorable trading conditions, minimal spreads and instant execution in transactions. The speed of withdrawal of profits is also important to me. That's why I chose fxopen.