I have one USB 2 and one USB 3 hub, both connected to a USB3 port of my mac. The USB 3 hub has a small number of ports, so I have to pick exactly what will use that hub. Both hubs are powered. I have one iPad 1, an iPad 2, an iPad Pro, an Apple TV4 and an iPhone 6. I develop apps for iOS, so I need these devices to be connected on the right hub for them. Will it make any difference to connect them on the USB 2 or 3 hub? I mean in terms of data transmission speed. I don't want to waste a USB 3 fast port on a slow device.
As of August 2017, only the 12.9” and 10.5” iPad Pro (not the 9.7” iPad Pro) support USB 3 transfer speeds. No other iPad, iPhone, iPod, or tv does.
This is confirmed by Apple’s Store page for the Lightning-to-USB 3 Camera Adapter:
The 12.9-inch iPad Pro and 10.5-inch iPad Pro transfer data at USB 3 speeds, while the 9.7-inch iPad Pro uses USB 2.
The problem is that the USB-to-Lightning cable Apple provides is only a USB 2 cable. You’d need a USB 3.0-to-Lightning cable, or some kind of adapter, to benefit from the greater transfer speeds. Those do not exist yet, and even Apple’s USB-C to Lightning Cable only supports data transfer at up to USB 2.0 (480 Mbps) speeds.
Furthermore, System Information lists my iPhone 7+ as having a maximum transfer speed of 480 Mbps when connected to one of the main USB 3 ports on my iMac. This is consistent with USB 2 transfer speeds, which confirms that so far, no iPhone supports USB 3 transfers, at least not with Apple’s official Lightning cables.
It’s unclear whether the 4th generation tv supports USB 3 transfers. It does include a USB Type-C port, but that doesn’t necessarily mean it supports USB 3 speeds. For what it’s worth, there’s a USB 2-to-Ethernet chip inside TV 4, per iFixit. I doubt Apple would include a USB 3 port in tv, when most users would rarely, if ever use it, while leaving other devices with USB 2 that would benefit from USB 3.
If you want to be certain, plug your tv 4 into one of your Mac’s builtin USB 3 ports, and check System Information.
In summary: Connect your Apple mobile devices to the USB 2 hub.