If you're looking primarily for notifications, I would focus on Series 1. It offers a faster processor and is very similar to the first Generation Apple Watch and will be supported longer likely with WatchOS updates. Also, there are some great sales on the aluminum model if you search. The First Gen Watch is still plenty capable of handling tasks, but has a slower processor, however, has excellent sale prices right now.
I own the stainless model which offers the sapphire display, which is highly Scratch resistant. The aluminum model offers a much lighter casing and the Ion-X Glass display, which is similar to the iPhone display.
The biggest selling points of the Apple Watch is the freedom of not having the iPhone tethered to you and the fitness tacking is very good. You also have the option of Apple Pay if you want.