Which is better for office work?

The Dell. Its 100 Hz panel and blue-light mode make long sessions easier, and DisplayPort gives you a cleaner connection to most business PCs.

Which has the better picture?

The Dell, on paper. It specifies a TN panel with 250 cd/m² brightness, 16.7 million colors and 170°/160° viewing angles; the JBL lists none of these, so its image quality is unknown.

Is the Dell worth stepping up to?

Yes for most buyers. You get a faster panel, an extra port and a monitor brand with support, which matters more than the small size both share.

Neither maker publishes a lifespan figure. Dell's monitor warranty and service network make a failure easier to resolve, which is the practical difference.

Can I use either for gaming?

Only for light or older games. Both are 1600x900 with 5 ms response; the Dell's 100 Hz helps, but neither is a gaming monitor.

Do both work with a laptop?

Yes. Both take HDMI, and the Dell also takes DisplayPort; the JBL adds VGA for older laptops and desktops.

JBL 20 Inch PC Monitor vs Dell Pro 20 E2026H Monitor

Buy the Dell Pro 20 E2026H for a main desktop monitor. It has a faster 100 Hz panel, DisplayPort plus HDMI and VGA, HDCP support and a blue-light reduction mode. The JBL 20 Inch is a basic 75 Hz 1600x900 screen with HDMI and VGA only, and JBL is not known for monitors, so support and panel quality are a gamble. Both are small, low-resolution TN-class displays; the Dell is the safer, better-connected pick.

Choose the JBL 20 Inch if you only need a cheap spare screen for a second PC or a basic office task and HDMI or VGA is all you will ever plug in.
Choose the Dell Pro 20 E2026H if you want the better panel, more ports and a brand with real monitor support behind it.

Prices

JBL 20 Inch PC Monitor: $69.95 at Amazon (last seen Nov 13)