He is better than yesterday. (he's ill) - you could also say "He is doing better than yesterday" or "He is feeling better than yesterday"
This is *the* fifth time I've called.
Your English is better than *mine*.
It sets a bad example *for* everyone
My cooking is worse than my mother's. (saying cooking again could be redundant, but your original was fine).
We don't have the least chance of winning this game. -There are a few ways this could be re-phrased to sound more natural:
"We don't have a chance in hell of winning this game" (somewhat vulgar, but probably most common)
"We don't stand a chance of winning this game" (your best bet if unsure of the company)
"We don't have a chance of winning this game" (a bit awkward, but still correct)