Amazon (AMZN) had the highest return in June 1998 by a large-cap US stock, returning 126.7%.

ASSET	MONTH	% RETURN
Amazon (AMZN)	June 1998	126.67%
MicroStrategy (MSTR)	June 1998	73.85%
Rambus (RMBS)	June 1998	61.39%
Ciena (CIEN)	June 1998	34.54%
Copart (CPRT)	June 1998	33.33%
Waste Connections (WCN)	June 1998	30.85%
ResMed (RMD)	June 1998	29.26%
Microsoft (MSFT)	June 1998	29.21%
Intuit (INTU)	June 1998	28.95%
NVR (NVR)	June 1998	28.82%
Fifth Third Bancorp (FITB)	June 1998	28.12%
Electronic Arts (EA)	June 1998	25.58%
SAP SE ADR (SAP)	June 1998	24.79%
Capital One Financial (COF)	June 1998	24.19%
United Rentals (URI)	June 1998	21.74%
Johnson Controls International (JCI)	June 1998	21.59%
Cisco Systems (CSCO)	June 1998	21.53%
Cognizant Technology Solutions Corp Class A (CTSH)	June 1998	20.63%
CoreSite Realty (COR)	June 1998	20.53%
Watsco (WSO)	June 1998	19.79%
Mueller Industries (MLI)	June 1998	19.77%
Reinsurance Group of America (RGA)	June 1998	19.14%
Check Point Software Technologies (CHKP)	June 1998	19.09%
JB Hunt Transport Services (JBHT)	June 1998	18.75%
Comcast (CMCSA)	June 1998	18.73%

Large-cap stocks are treated as having a market cap of $10B+.