The flagship Ambient Weather hardware today is the WS-2000. It is the newest.
The previous version was the WS-2902A and is still a current model a bit less price because the display is not as nice. The difference is just the display as the outdoor unit is exactly the same part. The WS-2902A is WiFi only and requires a smartphone to configure ...but is not required thereafter. The WS-2000 can be configured directly on the display console itself. The WS-2000 display is much nicer looking and is able to be viewed at different angles, where the WS-2902A display requires that you look at it a just the right angle to see the numbers or it gets washed out. The WS-2000 also supports extra sensors where the WS-2902A does not. The WS-2000 display console also supports an SD card and has internal logging where the WS-2902A display is just for live data and keeps some historical stats for high/low and rain totals, but not a full historical record. With the WS-2902A all your historical is just online with the different services. You can can have multiple displays with either model. You can even mix both types of displays with the same outdoor unit. So essentially you can upgrade a WS-2902A into a WS-2000 just by buying the WS-2000 display (but it isn't for sale separately yet).
The WS-8478 has not been a popular seller at all. Its main advantage was that it could support extra sensors and it was released around the same time as the WS-2902. But now with the WS-2000 there really is no point to the WS-8478 and it lacks solar radiation (it has UV index only).
The WS-1000 series is a prior generation. The newer WS-2xxx series is much much more reliable and uses better sensors.
All of these use super capacitors with a solar panel for charging. But they also have a compartment for Alkaline or Lithium AA batteries (non-rechargeable) for backup for those times when there isn't enough solar power to keep the super capacitor going.
Besides these that we have discussed there is also the WS-1550-IP. That is basically the same newest outdoor sensor array with no display console and instead it uses a device called the ObserverIP which requires Ethernet connection. The existence of the ObserverIP is not something to be dismissed so quickly because it isn't a display. The ObserverIP allows another device on the network to read live data from it. This could be a Meteobridge or a computer running one of various weather software programs to then allow you to do much more with your data, like create your own website, or send the data to other online services, or backup your data to SQL database. The good news is that just like you can add multiple displays to the WS-2xxxx models you can also add an ObserverIP and give those stations the ability to have these extra features too. The ObserverIP requires an extra indoor sensor model WS-1000-BTH for pressure, temperature and humidity.
So no matter which you initially go with WS-2000, WS-2902A, or WS-1550-IP you can mix and match and upgrade any one of those to become more by adding the missing parts. Therefore there is no better one between the WS-2000 and the WS-1550-IP as they have different capabilities....but you can more easily today give the WS-2000 the WS-1550-IP capabilities because you can buy the ObserverIP, but for now you can't buy a WS-2000 display console to add to the WS-1550-IP (but hopefully soon you will).
