Which is better for a modern 1080p TV?

The Panasonic. Its 1080p upconversion corrects brightness pixel by pixel, so DVDs look sharper on a flat panel. The onn. sends standard DVD resolution over HDMI.

Can the onn. play MP3 or JPEG files?

No. It is a DVD player only. The Panasonic plays MP3, JPEG and Xvid from disc or a USB stick.

Which one lasts longer?

Panasonic has a long track record of reliable DVD decks, and the S700 is a full-size unit with more room for cooling. The onn. is a light budget player; its 4.4 rating suggests most owners are satisfied, but it is built to a lower cost.

Is the Panasonic worth stepping up to?

Yes if you watch DVDs on a large TV or want to play music and photo files. If you only occasionally play a disc on a small TV, the onn. covers that.

Does the Panasonic come with an HDMI cable?

No. The onn. includes a 6 ft HDMI cable and a remote with batteries. Budget for a cable with the Panasonic if you don't have one.

Can either player record DVDs?

No. Both are playback-only. The Panasonic can copy audio CDs to a USB stick, but neither records video to disc.

onn. HDMI DVD Player vs Panasonic DVD-S700 DVD Player

The Panasonic DVD-S700EG-K is the better player for most people. It upconverts DVDs to 1080p, plays MP3, JPEG and Xvid files, and can rip CDs to a USB stick. The onn. is a simpler, lighter player that plays DVDs and little else, though owners rate it well for easy setup with the included HDMI cable. Pick the onn. only if you want the cheapest working DVD player and nothing more.

Choose the onn. HDMI DVD Player if you just want to play DVDs on a TV with the cable in the box and don't need upscaling or file playback.
Choose the Panasonic DVD-S700EG-K if you want 1080p upconversion, MP3 and JPEG playback, and CD ripping to USB.

Prices

onn. HDMI DVD Player: $49.85 at Brands For Less USA (checked today)
Panasonic DVD-S700 DVD Player: $70.60 at Antonline (checked today)
Difference: the onn. HDMI DVD Player is $20.75 cheaper than the Panasonic DVD-S700 DVD Player today