Personally, I find the Mini more than adequate, but others prefer the full fat version.I still use a Mini 4 which I only use in the aircraft, battery life is around 4 hours and is generally fine. Like all iPads, it hates being left in the sun, when it's prone to overheating.
I guess it's down to personal preference. Assuming it's still the same, the one thing I would recommend is to go for a cellular version - not that you necessarily need a SIM card but the cellular models also have GPS. I also have a PilotAware for traffic alerts, but I find this doesn't sync [properly with the iPad maybe 20% of the time, so end up using the iPad's GPS functionality.