Oddsmonkey is potentially a LOT more powerful if you have the time. Nothing flows however, you have to do everything manually and enter numbers in different calculators and whatnot. On Yesbets I click on an offer, the matches appear there on the same screen, I pick one, and it spits out the back and lay figures. 5 second process at most. Oddsmonkey requires you to find the offers, then use the oddsmatcher to manually find matches, then use a separate calculator to calculate the lays, etc. It does have tools which Yesbets doesn't but for me (limited time) the time saving on Yesbets is invaluable.
Oh and Oddsmonkey never has all the offers. Yesbets always has loads more listed.