There are many factors that determine could "best", but the basic criteria you should look for is longevity of network, support, variety of offers, pay competitiveness and simply reliability. It is easy to get sucked into "best new shiny network" and only to discover you not getting paid cu they went belly up or juts took money an d opened new dba.
I suggest you stick with more popular at the beginning, as mentioned above, than move on to more specialized ones. All best to you and good luck.