The best broker should have the following features; so far many brokers have these features, personally, I use FreshForex
1. Maximum leverage of 1000:1
2. Minimum lot size of 0.1
3. No stop loss hunting
4. No markup on spread
5. Low commission
6. No slippage
7. No re-quoting
8. Low swap
In my opinion you should add regulation as others suggested and a true negative balance protection.