Ipads are great, but….
There are tons of options when it comes to portable GPS units. One of your best bets is to purchase an iPad or Android Tablet and dedicate its use just for your navigation app (such as Foreflight, Garmin Pilot, or WingX Pro). There are also separate GPS only units you can buy (like a Garmin 696). The advantage of the standalone unit, like a Garmin 696, is that there is no other software on it and it will probably work great as a GPS and nothing else (which is most likely what you want).
The advantage of an Ipad or Android tablet is you can do a lot more with them (like multiple apps or internet and email). You can also switch software, easily upgrade to the latest and greatest software, and even combine your logbook into an electronic app.
Whichever you choose, remember this: there is NO FAA approved portable electronic GPS that you can legally use to navigate under IFR. To be able to file “direct” or accept direct to most fixes, you will have to have a panel mounted, TSO’d, FAA approved GPS receiver (like a Garmin 430, 530, 650, etc). Don’t let anyone try and tell you your iPad will ever be a legal way to navigate under IFR, it won’t (although it is still a great situational awareness tool!)