If you just want a general idea where you are, a rough approximation of speed, distance, etc then just using apps on your Android phone are fine. Google Maps just added terrain visualizations and the ability to see sat imagery where you are is always nice. Google MyTracks adds more GPS handheld type functionality. There are probably other apps out there now but just starting out with the free Google apps is good way to start. The cell phones apps are nice that as long as you have wireless coverage you can have the most recent maps and info that you need.
The downside is unless you preload some maps, you can easily loose wireless coverage in the boonies, which can map the app useless or reduced. If you want speed, distance, etc then the GPS needs to be on all the time which will burn down your batteries. The phone really needs to be in a waterproof bag or box. My phone really gets hot when inside one of the Aquapac cell bags with the GPS on. Probably not the best for the longevity of your phone. Overall, the phone isn't bad --you usually have it around and it is nice and easy to use but I found it best to leave off and only use it on occasion. I would never count on it working in an emergency but nice to have for backup or for fun.
The handheld GPS units are build more for the trail. Pretty much all of them claim to be waterproof, rugged, battery life is better plus you can take along extra batteries if needed. The maps are pre-loaded and they have better hardware/software for dealing with poor GPS signals they are better for more rural areas or water where you may be far enough from cell towers. You can depend more on the handhelds then the phone versions. Still would want a map and compass as backup.
Don't expect a handheld to work like your auto GPS, which is fire it up and you are good to go. But for a handheld GPS often the basemaps are useless. You will need to spend sometime figuring out what maps you want to add and buying map packages can get expensive and you may have to buy maps again if you need updates. You can also be disappointed to find out that coverage in your area is spotty with say trails, points of interest, roads, lakes, fishing spots, etc, after spending a $100 on a map. There are free maps -- gpsfiledepot but you need to spend time finding what maps you like and need.
I have yet to dunk my Garmin Oregon but even though it seems that most GPS are waterproof the word on the street is you should keep them in waterproof bag, even the GPSMAP76 or 78 which are some of the few that float.
Overall with the handheld you get a much more customizable unit but you will need to invest more time and money. If you expect to just turn it on and leave it at that then I would stick with the cell phone or a basic GPS.
I went for recently for kayaking, hiking and biking a Garmin Oregon 450. I have a number of free topos from GPSFileDepot and paid for the Garmin BirdsEye sat imagery subscription. I downloaded the sat imagery for the areas I bike, hike and kayak and use them with the topo maps. This seems to serve my needs for kayaking on streams and lakes around here. I don't do open water so not sure what maps are best there.