Cisco Systems (CSCO) had the highest return in April 1991 by a US stock in the S&P 500 (GSPC), returning 23.9%.

ASSET	MONTH	% RETURN
Cisco Systems (CSCO)	April 1991	23.91%
Brown & Brown (BRO)	April 1991	22.46%
Advanced Micro Devices (AMD)	April 1991	20.99%
Carnival (CCL)	April 1991	20.5%
Paramount Skydance Corporation Class B Common Stock (PSKY)	April 1991	19.19%
Fair Isaac (FICO)	April 1991	18.65%
Constellation Brands Inc Class A (STZ)	April 1991	18.11%
JPMorgan Chase (JPM)	April 1991	17.98%
Best Buy (BBY)	April 1991	16.68%
Lam Research (LRCX)	April 1991	15.84%
Hasbro (HAS)	April 1991	15.63%
PulteGroup (PHM)	April 1991	15.52%
Pentair (PNR)	April 1991	15.39%
Smith AO (AOS)	April 1991	14.67%
Electronic Arts (EA)	April 1991	14.09%
IDEX (IEX)	April 1991	13.45%
Jack Henry & Associates (JKHY)	April 1991	13.19%
West Pharmaceutical Services (WST)	April 1991	13.11%
Motorola Solutions (MSI)	April 1991	13.1%
KLA-Tencor (KLAC)	April 1991	12.94%
Tyson Foods (TSN)	April 1991	12.7%
Lennar (LEN)	April 1991	12.51%
General Dynamics (GD)	April 1991	12.32%
ONEOK (OKE)	April 1991	11.65%
Vulcan Materials (VMC)	April 1991	11.64%