My favorite is the card game; I don't care if it's small, medium or large. I feel that playing games where I have to remember where each card is, is good for keeping my memory sharp.
My second favorite is the pipes. The trick to that, True, is start from the bottom.
Also, there are only a limited number of patterns, so once you learn them, you learn to recognize which one it is. Some of them unfortunately take a while for the water to go through the pipes (and you can't minimize the page, or switch to another browser tab, or the water stops flowing), and I sometimes don't want to take the time. So when it's one of those, I will refresh for something else.
The match 3 is fun, and I play it sometimes. I usually prefer the smaller boards. 
I love the snow game, at least in the Christmas present format. Even though it takes a little longer than most of the games that I play, I like the graphics for it.
Although sometimes I won't play it when I'm pressed for time.
The ones I never play are the picnic (hidden object) game, and the stepping stones. Even though I know where all the objects are in the picnic page, sometimes when I click the correct object, it says I didn't, and then I have to start over. I HATE that, so I just won't bother with that game anymore. The stepping stones used to be one of my favorites, but I just haven't played it in a while, I'm not sure why.
I also don't play the new one that often. I don't like how random it is. Sometimes I have all but one or two flowers, and then I have to wait, and wait, and wait, and wait, until the final flower(s) come up. My best friend gets frustrated with it, because on her computer her mouse is either unreliable or slow, not sure which, but she can almost never click the flowers in time.