Now, you will definitely buy Apple Watch Series 3 as Apple has already managed to cope with all cellular connectivity problems that existed before. With watchOS 4.0.1 all these widely known issues were completely removed.
Apple Watch users always faced problems which were connected with its switching to a Wi-Fi connection. Connection problems were caused by Wi-Fi hotspots such as hotels and coffee shops that displayed a confirmation webpage. The Apple Watch connected to free Wi-Fi by mistake but it couldn`t see confirm or page that made it impossible to connect either to LTE or to Wi-Fi. This device just preferred to choose Wi-Fi in order to save battery.
Fortunately, watchOS 4.0.1 is aimed at solving this annoying problem. Make sure that your Apple has 50 percent charge and is connected to the charger. Then download and install watchOS 4.0.1 update on your iPhone by using the Apple Watch app. Just tap General > Software> Update to launch it successfully. All you need to do is to make sure that this update is really capable of fixing this cellular issue and making your Apple Watch work at its full capacity.