I get a lot of questions about which MIDI interfaces work well with Patch Base, so I will work on getting a list on this page.
The bottom line is that any MIDI interface that correctly supports sysex data should work with Patch Base. However, I highly recommend using a wired interface (as opposed to wireless, such as Bluetooth) if you are going to be sending or backing up banks of patches for your synths. Wireless interfaces can lose MIDI data during transfer, meaning that you won't get a complete bank transfer sometimes when using them. This is just a limitation of wireless MIDI. With a wired interface, this doesn't happen.
Lightning MIDI Interfaces
I own and regularly use the iConnectMIDI1 from iConnectivity. It plugs directly into your iPad or iPhone and doesn't require any external power, so it's about the simplest MIDI interface setup you can have.
Older iPad (30-pin connector) Interfaces
If you have an older iPad (with the 30-pin connector instead of the newer lightning connector), the Griffin MIDIConnect will plug directly into your iPad.
Bluetooth MIDI Interfaces
I also have the Quicco mi.1, which is a small bluetooth MIDI interface that's easy to use as well. It's powered by the MIDI port of the device you plug it into, so it's a great, portable solution for connecting to your iPad. With the latest firmware update (2.2.1), it establishes a solid MIDI connection that supports sysex and works well with Patch Base.