my experience IB and dukascopy I have both live account with them ,and i am a highly frequency daytrader, here is my opinion,
gbp/usd spread:duka a little better then IB(especially asia session duka 0.5~1pips better then IB ,other time almost the same)
eur/usd spread:IB better then duka (asia session almost the same,other time IB 0.5pip better)
liquidity:IB better then duka(no need to worry if the size under 1 million unit)
execution:both the same ,IB hotkeys is great but its platform is too complicated for a beginner
commission:duka 15usd/m,IB 20usd/m(there is a way to reduce an half commission in duka,find an introduce broker and make a deal with him,it is great for highly frequency trader)
so,i recommend duka for gbp/usd,IB for eur/USD. If duka's banking license is approved ,i highly recommend to give duka a try. I am pretty sure their spread are the best among the ecn platforms.
BTW: hotspot fxi(institute)used to have the best spread before,but now not any more,anyone have experience with it?