Apple Watch series 8

It basically comes down to if you want the ability to make phone calls on your watch without being near your phone. If yes, get the cellular. If no, don't. If you think you might want that feature in the future get the cellular. You don't have to enable a cellular plan on the phone until you want to.

As long as your iPhone is nearby, the GPS only can do EVERYTHING the cellular can do by piggybacking off of the iPhone radios. Where nearby is the Apple Watch and iPhone are in the same moderate sized wood frame construction home.

And the GPS only is less expensive, plus no monthly cellular fee (typically the cellular fee is $10 U.S; depending on the carrier and if the carrier even supports the Apple Watch).

The cellular model will allow you to leave your iPhone at home when you go for a walk, run, bike ride.