For small punters like myself there isn’t a great deal of difference between the two, I bet in US Dollars and the minimum on Betfair is US$4 per bet. This is a rule that Betfair sticks rigidly to, whereas Betdaq has a similar minimum but they don’t seem to reject bets of a lesser amount. This Betdaq lenience allows me to bet on multiples if the fancy takes me, without racking up large $ bets. Also Betdaq has a much better facility for selecting multiples.
Overall my recommendation for fellow punters would be to have accounts on both sites, as sometimes the odds on offer can vary between them, allowing the reader to pick and choose.