Have found some spreadsheets of data on this page (black links in the middle of the page)
That data may not be from online gambling but it may give you some point of reference.

From my own perspective I can tell that I always bet on dice games with odds lower than 50/50. With promotion money (or faucet) I go for max multiplier.
Huge win, isn't it obvious? Happiness, equal to the amount won and a little more betting, just to equalize the balance(even number of credits). Bigger losses get me discouraged quickly, usually I end at two consecutive losses.