I recently when through the same dilemma. I wanted to see if I could use a
relatively inexpensive (more) modern device such as an iPhone or Android.
My reasoning was that these devices have built in GPS, Bluetooth, and WiFi
(albeit wifi is not necessary). Another reason for going this route was
that the Nokia Here app is free and allows you to download maps and
navigate offline (without Internet access).
So I tried an older iPhone 4 which I had and was no longer being used.
Because I am now at an age where I need reading glasses, an iPhone 4 or
even 5 was too small to read without my readers which I can't wear to
drive. But if you have good vision or wear contacts or even prescription
glasses all the time this might be a great solution.
What I wound up using was a 7" tablet. I was able to get a
refurbished Dell Venue 7 for ~ $80 at Best Buy (online) which works great
for me. Using an android not only allows me to use Here (offline) but I
also have the option of tethering from my phone in which case I can use it
online which shows traffic. If you tether you can also use any other
mapping software as long as you can turn off pop-up messages. One other
plus of using an android is you can install Google Tracks which tracks your
trip and displays on Google maps.
In case you are wondering I used an ram mount to hold the tablet which
works great. I also installed a USB port so I can keep it charged up while
riding. Oh and I keep a plastic freezer bag handy in case it rains. I just
throw it over the tablet.