I love my soda siphon! I got a stainless steel one for Christmas, and I've been using it non-stop since. It's much easier for me. Since I don't have a car every time I wanted to buy a case of bubbly water I had to talk someone into driving me to the grocery store. This way I only have to buy a box of CO2 cartridges which fit into my pocket, and I can have bubbly water whenever I want! Plus, this way I don't have tons of glass or plastic bottles in my recycling. Because recycling is good, but not using it at all is better. Words of wisdom y'all. Words of wisdom.
One day I may move up to the Soda Stream, but it takes a lot of room up on the counter, and I already have a lot (LOT) of kitchen appliances. The CO2 is a lot cheaper with the Soda Stream - $34 for 60L using the soda stream vs about $72 for the equivalent amount for the Soda Siphon. Another pro is the ability to fizz up multiple bottles of water at once, and keep them all cold in the fridge. This is mostly only needed for parties though, otherwise I don't find I need more than one bottle at a time.
My siphon is the one litre ISI Soda Siphon. It's wicked.
Image: John Burgoyne via