T-Mobile US (TMUS) had the lowest return between 2008 and 2009 by a mega-cap US stock, returning -61.1%.

ASSET	YEARS	% RETURN
T-Mobile US (TMUS)	2008-2009	-61.09%
Bank of America (BAC)	2008-2009	-60.59%
GE Aerospace (GE)	2008-2009	-54.84%
UnitedHealth (UNH)	2008-2009	-46.58%
NVIDIA (NVDA)	2008-2009	-45.24%
Morgan Stanley (MS)	2008-2009	-41.18%
Merck (MRK)	2008-2009	-30.78%
Berkshire Hathaway (BRK.B)	2008-2009	-30.68%
Berkshire Hathaway (BRK.A)	2008-2009	-30.04%
Eli Lilly and (LLY)	2008-2009	-26.34%
Exxon Mobil (XOM)	2008-2009	-24.43%
HSBC Holdings PLC ADR (HSBC)	2008-2009	-24.32%
Shell PLC ADR (SHEL)	2008-2009	-20.83%
Goldman Sachs (GS)	2008-2009	-19.74%
American Express (AXP)	2008-2009	-18.38%
Toyota Motor Corporation ADR (TM)	2008-2009	-17.4%
Thermo Fisher Scientific (TMO)	2008-2009	-17.32%
Caterpillar (CAT)	2008-2009	-15.81%
Procter & Gamble (PG)	2008-2009	-13%
Costco Wholesale (COST)	2008-2009	-12.95%
Chevron (CVX)	2008-2009	-12.34%
Cisco Systems (CSCO)	2008-2009	-11.33%
Microsoft (MSFT)	2008-2009	-11.23%
Alphabet Inc Class A (GOOGL)	2008-2009	-10.52%
SAP SE ADR (SAP)	2008-2009	-6.77%

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