I would prefer Binexx over Binarybet. For one thing Binexx is an exchange whereas Binarybet acts as market maker, you have to take what Binarybet quotes you.
Binexx's volume is low, if it were higher it might be better. I think it needs to attract more customers and do something about the prices at 0-10 and 90-100 levels.
Intrade is very similar to Binexx, for the daily Dow Jones contracts they are active usually during the last hours before contract expiry. Using a simple strategy I think the maximum, with certainty, under current liquidity that one can reasonably expect to make is about a few hundred to about one to two thousand dollars per month profit, even if starting with a small account and compound the profits upwards to the maximum.
I like the Spreadfair's financial trading platform style, but I don't have an account with it.