BOOK now or play the waiting game? That’s what a lot of travelers planning a trip to Europe this summer are asking themselves as they watch the price cutting that has gone on among the major airlines this spring, yielding some pretty sweet deals for bargain hunters. In recent weeks, travelers have been able to find nonstop round-trip flights, including taxes and fees, for $477 from Chicago to Madrid for travel in April, $312 from Newark, N.J., to Dublin in May, and $482 from Washington to London