Dunno if you have come to a conclusion, but I would go for Android.
The c:geo app is unbeatable, although a bit slow to load. Most androids have a-gps support, and are relatively quick and accurate and you always have them on you.
Depending on your country, you may be able to get good data plans. I am in the UK, and get unlimited net. No advertising now!!
You may wish to purchase some extra, high-capacity batteries for your android. 3 in total should be good for a day or 2...
(2 spare, 1 in phone).
Thanks for reading,
Liam