I haven't used either one for outdoors, but I've had pretty good luck with a cheap-O party fog machine for indoor shots.
My cheap fog machine will make a small amount of fog that makes discrete wisps and rising curls. It's a little flaky to use (it only runs when you mash the button about 75% of the time) but I love the effects it makes.
My "big" fog machine will fill a room with haze, which is a totally different look. (and it'll set off the smoke alarm if you try to haze up the house for my Halloween party, but that's a different story).
It's important to remember this part of the description from the "Haze in a Can:"
"Back lighting and position of lighting will determine how thick the haze or fog will look. Colored lights will enhance color of complete cloud, haze or fog."
For the most dramatic smoke and fog effect, put a light behind the fog, just out of frame, pointed forward in the general direction of the camera. Use a colored gel on the light to get really cool color effects.
I can't link directly to it from here, but if you look in my Flickr (see signature), go into the "Dragoncon 2013" album, there are some Wicked Witch photos where I used my little fog machine. It was pouring rain outside, so we just shot them in my hotel room with the hotel drape for a backdrop.
Also note: If you want low-lying ground fog, you'll use a fog machine and a fog chiller: It's a box of ice which will chill the fog so it's cooler/denser/heavier than the ambient air, so it'll creep along the ground.