Best soda maker on the market?

I agree with the siphon because you aren't opening and closing a bottle so if you don't drink it all it won't go flat. Although if you drink the entire thing in a day or so it doesn't matter.

However, I have the isi siphon and it leaks A LOT each time I charge it. I haven't found others that have this problem though. I even fill it only 3/4 full (cold water). So if anyone has any tips for me I'd appreciate it!

I am assuming you mean soda water and not sugar drinks. If that is the case I've used Isi brand for years. Don't discard the fact old antique glass siphons still work excellent if you can find at an antique store. Isi cartridges will fit them too!

Thanks for the suggestions! I was thinking siphon because nobody needs an extra appliance taking up counter space, but maybe it makes more sense to do the sodastream with its multi-use cartridges.

Soda stream..you can adjust the amount of carbonation. As mentioned the 'penguin' is the better model as it uses glass bottles---the plastic ones need replacing after a couple of years. ( think there's another model that uses the glass ones now)
Bed Bath and Beyond will sell the charges...get another empty one so they have one filled at all times. Cheep with the 20 percent coupon they spam mail you. About 13 bucks with the exchange and coupon.
I don't know if they carry the penguin--but Williams Sonoma has those.
In the long run it's better than a siphon as those little cartridges are single use only.
The stream lasts us a couple of months using it everyday.

You can also mimic sparkling mineral water by adding a pinch of baking soda and a few grains of Epson salt to the water to give it a softer rounder taste.

The penguin! Definitely splurge a little on the penguin. Besides looking better on your kitchen counter, it's sturdy and pretty fool proof. I love the airtight bottles it comes with, perfect for carrying around.

Soda stream might be optimal for a gift because it's more if a one button press, easy operation. Additionally, they have syrups you can even buy if they really don't like to cook at all but might want to experiment with their own sodas and various sparkling beverages.
If they are more adventurous culinary types however, I would go the isiWhip route with CO2 cartridges because it's much more versatile. You can carbonate sodas of course, but you can also even make bread really quickly by using the CO2 to leaven rather than yeast an then microwaving to cook. It's an Adria method. You can read specific instructions in the Voltaggio brothers' cookbook, VoltInk.

I have a Soda Stream. It's a very well thought-out and designed product, works well, and the cartridges aren't too expensive as long as you return your spent cartridges. That said, it has none of the charm or handsome design of some of the siphon style ones.