The top one is a counter pressure bottle filler
You flush the bottle with CO2, then pressurise, then fill under pressure by slowly bleeding off pressure
This is better for long term storage as a more sure fire method to avoid oxygenation
However it is a slower method
The bottom one is a bottle filling gun
you can still flush with CO2, but it isn't done under pressure, so it can lead to excessive foaming
It's a faster method, but does have a little bit more risk of oxygenation
I prefer the top one, I've got one that I bottled 200 grolsch flip top bottles for my wedding with (after filtering then force carbonating in kegs), took a full night of work with some mates helping me, but wasn't too bad really