I much prefer my tablet for filling out reports either in apps or the web page based reporting tool (SASSIE etc). Much larger screen to see things. Also I tend to use my tablet to take pictures as it's a Samsung and my cell phone is a cheapo - Schok (yes that's the brand phone I have). I can also more easily see and crop photos on the larger screen.
Be aware, I have experienced some, very few, apps don't function on my tablet for some reason. I think it's a developer (coder) issue.
I find many of the places that I would be filling out the reports, like fast food joints, provide free WiFi. So does Starbucks, Dunkin Donuts, Barnes and Noble, Walmart, and most grocery stores. Therefore you don't necessarily need to have the table on a data plan. This would save you about $20 per month depending on your cell provider.
Also, tablets that are WiFi only are cheaper (iPads included) than those that have the capability to connect to cell towers.