Use of the cell phone is safer, Make sure the Wi-Fi side is encrypted (Password or decryption key needed to access) and change the password/code/key from time to time.
Or better yet, Do the financial stuff using the phone's browser.
But be aware.. You have to decide how heavy a tin-foil hat you need is.. That is to say NOTHING, Not even handling all financial transactions in person at the teller's cage, is 100% safe.. So you evaluate the risks and act accordingly, Review your statements often (like every week at the least if not more often) and if transactions show up that look strange.. QUESTION THEM.
True story. Friend and co-worker rented a car.. Shortly after she got a call from her bank about a suspect transaction.
When UPS delivered the goods, the thief signed for them. The UPS person who delivered then stepped aside and his "Ride along" Stepped up and explaned the thief's fugure to him.. also his Miranda Rights. (She's a cop).
She then went to the auto rental where thief's brother worked and explained his future, and Miranda rights, to him.
The family that goes to prison together.. Stays together.