Which is better for watching DVDs on a modern TV?

The onn. It ships with an HDMI cable and outputs 1080p over HDMI, so it connects to a flat panel in one step. The GPX also has HDMI, but you supply the cable.

Can I use wireless headphones with either?

Only the onn., which has Bluetooth 5.0. The GPX DH300B has no Bluetooth, so you would need wired headphones through your TV or receiver.

Which plays more disc types?

The GPX DH300B. It handles CD-R/RW and DVD-R plus JPEG photo files. The onn. is listed for DVD playback only.

Which has better surround sound?

The GPX DH300B names Dolby Digital decoding, which suits a receiver setup. The onn. passes audio over HDMI but lists no surround format.

Is the onn. worth stepping up to over the GPX?

Yes for most people. Bluetooth, USB, parental controls and the included cable add real everyday use. Pick the GPX only if Dolby Digital or photo playback matters more.

Which is easier to set up?

The onn., because the HDMI cable, remote and batteries are in the box. The GPX needs an HDMI cable you already own.

onn. HDMI DVD Player vs GPX DH300B DVD Player

The onn. is the better pick for most shoppers. It adds Bluetooth 5.0, a USB input, parental controls, a bundled HDMI cable and a remote with batteries, and its 4.4 rating across more than 4,300 ratings shows owners are broadly satisfied. The GPX DH300B is a plainer front-tray player with Dolby Digital and JPEG photo playback, but no Bluetooth, no USB and a heavier build. Neither is a premium machine; both are basic 1080p DVD players.

Choose the onn. HDMI DVD Player if you want Bluetooth audio, a USB port, parental controls and a cable in the box.
Choose the GPX DH300B if you mainly want a simple front-loading tray player with Dolby Digital and JPEG photo slideshows.

Prices

onn. HDMI DVD Player: $49.85 at Brands For Less USA (checked today)
GPX DH300B DVD Player: $45.00 at The Home Depot (checked today)
Difference: the GPX DH300B DVD Player is $4.85 cheaper than the onn. HDMI DVD Player today