None at all. All welcome bonuses from the 5 brokers cannot be withdrawn immediately but must be used for trading first. It is the profits earned that can be withdrawn.
Believe it or not, you can ask the broker directly. Some ECN/STP brokers openly state that they mark up spreads because they feel they have the right to do so.
You can also check the authenticity of spreads from an ECN/STP broker that (perhaps) covers up its spread mark-up by directly comparing the broker's spread with the actual market spread.
Some brokers offer PayPal because it is considered a trusted e-wallet company with high-quality services and many internet users are already familiar with it. Among those brokers are FxPro and eToro.
Each broker imposes different policies regarding the PayPal service. FxPro for example, would charge the clients a deposit fee of 2.7% and a processing time of at least 10 minutes, whereas for withdrawal, it is free of commission but takes at least 1 working day to process.
A-book broker is where orders go directly to the market, while B-book is where orders remain in the company.
A-book companies usually get profits from the spreads and commissions, whereas B-book companies get profits from a financial outcome (everything that a trader lost, the company gained, and vice versa).