There is no answer. One place is cheaper for one thing another place is cheaper for others. I like Bikewagon, Modernbike, Velomine and Ebay.
And for the record the stuff I've ordered from Merlin and Ribble has gotten to me within a week and well worth the wait to get a 105 group for $400 and an Ultegra crankset for $120 with free shipping from both places