I use a iPhone 6s and a H2O gps fishing and hunting. I have the Navonics app on the iPhone. The iPhone's GPS always seems to find me even in poor cell reception area but will not always load maps or will be incredibly slow. H2O GPS has the maps in it but needs more time to acquire satellites on start up. Accuracy is about equal and is usually with in 5-15 yds depending on the lake and accuracy of the lake map. The Navonics app is much better for searching out new lakes and updates often with no additional charge. The H2O is much better for setting way points and tracking. When hunting,if I have good service, I prefer the iPhone because of the satellite images I can see clearings, roads,water etc ahead of me when cutting cross country. Also the compass is very accurate on the iPhone and lighted. With poor cell service the H2O is the choice. To me it's a question of which is the best for where I am now and what I am doing.