American Express (AXP) had the highest return in April 2009 by a mega-cap US stock, returning 89.1%.

ASSET	MONTH	% RETURN
American Express (AXP)	April 2009	89.05%
Intuitive Surgical (ISRG)	April 2009	54.37%
Wells Fargo (WFC)	April 2009	45.84%
Bank of America (BAC)	April 2009	38.45%
Salesforce (CRM)	April 2009	36.95%
Caterpillar (CAT)	April 2009	31.05%
JPMorgan Chase (JPM)	April 2009	30.72%
GE Aerospace (GE)	April 2009	27.65%
Royal Bank of Canada (RY)	April 2009	25.14%
Lam Research (LRCX)	April 2009	24.41%
Micron Technology (MU)	April 2009	23.86%
Goldman Sachs (GS)	April 2009	23.44%
ASML Holding NV ADR (ASML)	April 2009	23.18%
Citigroup (C)	April 2009	22.98%
Walt Disney (DIS)	April 2009	22.21%
HSBC Holdings PLC ADR (HSBC)	April 2009	21.17%
Advanced Micro Devices (AMD)	April 2009	21.14%
Apple (AAPL)	April 2009	20.89%
Toyota Motor Corporation ADR (TM)	April 2009	19.63%
Visa Inc Class A (V)	April 2009	18.65%
Taiwan Semiconductor Manufacturing (TSM)	April 2009	18.5%
NVIDIA (NVDA)	April 2009	17.88%
Cisco Systems (CSCO)	April 2009	17.02%
Applied Materials (AMAT)	April 2009	15.73%
Alphabet Inc Class A (GOOGL)	April 2009	15.18%

Mega-cap stocks are treated as having a market cap of $200B+.