Unfortunately the other betting exchanges have far far less liquidity than Betfair, and much of the bets on offer are from bots that are simply mirroring the odds on Betfair (with their own margin added on)
Basically, all the money goes on Betfair because that’s where all the money is. It’s a vicious circle, great for BF and very difficult for any competitors to break in to the market.
Betfair is for sure the most liquid. Smarkets and Matchbook are growing. I've not used Betdaq.
However, if people are worried about hitting the Premium Commission levels on Betfair, and the other exchanges are mirroring prices, then surely it's worthwhile spreading stakes around.
Basically, all the money goes on Betfair because that’s where all the money is. It’s a vicious circle, great for BF and very difficult for any competitors to break in to the market.