The LTE connection will cost you about $10 a month at most carriers, and the LTE model does cost more. There's a non-LTE version, too, if you're not interested in the new feature. Most people probably don't need LTE, frankly, unless you regularly go on hikes or long runs and you don't want to be weighed down with your phone. Still, it's a nice option to have.
Our top pick for most people is the Apple Watch Series 4 with GPS (starting at $399), which has a huge display, ultra-fast processor, Raise to Speak Siri, fall detection and a built-in electrical heart rate sensor for taking on-the-go electrocardiograms. It also runs watchOS 5, which makes the watch even more useful with automatic workout-tracking, offline podcast playback and a Walkie-Talkie voice chat feature.