If you have the option to sign with any of these networks, I would cross Machinima off the list immediately. Unless you want to be signed with them for 3 years with no options to back out, and a low cpm, with little to no support, and they do almost nothing for your channel. I don't know a whole lot about TGN, Socialblade, and Fullscreen, so if you have access to their contracts, read through them carefully, and compare them. Which contracts offer you more, which company legally states more bonuses for you, such as channel support, advertising opportunities, etc. If things in the contract are confusing you, try to get in touch with support from these networks. If their support doesn't answer you with 1-2 days, that's a bad sign in itself. Weigh your options, take your time, and choose carefully! Having an option to back out of the contract with a 30 day or 10 day notice is always a huge plus too!