Assuming you don't want to use it for much else, a basic mini-ipad should be fine, but I'd go for the middle one (small middle and large is basically 16 32 or 64 gigabyte storage). The only other decision is whether you go for internal GPS or connecting to an external device via blue tooth. If you go for self contained then you can add a SIM card should wish to and use 4G, when away from Wi-Fi, for internet connection.
I have a middle size with SIM card and it's very convenient both on the ground and in the air.