I had the following combo
32gb cellular iPad 1 - 16gb iPhone 4
32gb tmo iPad air - 16gb iPhone 4
32gb tmo iPad air - 64gb iPhone 6
Beyond touch ID, I don't have a lot of desire to update my iPad. This one works great. That said, I would choose the iPad update over the phone... Except my kids are using a 3GS and um, the battery is shot and it needs help.
SOOO, I might have to update the phone to at least a 4s/5.
Basically, I use my iPad more each day than my phone, and I use my phone more as a phone than anything else. So the iPad would come first.