Only stayed in 3 but all were really nice: Sheraton Park Sydney (c'mon oysters/shrimps and free flowing booze during happy hour is frankly immoral!) - we got nice upgrade to suite; Sheraton Sopot (nice lounge and good breakfast. I'd go off season as the clientele otherwise is somewhat weird to put it mildly); Sheraton Warsaw (good hard and soft product although we prefer Marriott due to location)