Best Payment Processor for Invoicing

[Markey]

Hi,

I'm a self learned freelance software developer. I've been doing this for few years now mostly through Upwork, have a great history and huge network of people. I always accept payments through Upwork, which is kinda costly because their fees are huge rangin from 20%-10%.

I wanted to change something and try processing the payments by my own.

I don't have a company, I'm an individual (US Citizen, I have SSN). What payment processing companies are the best and is easy to register without any hassle?

Thanks in advance.