Zillow (ZG) had the highest return in April 2014 by a large-cap US stock, returning 22.8%.

ASSET	MONTH	% RETURN
Zillow (ZG)	April 2014	22.76%
AstraZeneca PLC ADR (AZN)	April 2014	21.19%
Centrais Electricas Brasileiras (EBR)	April 2014	19.66%
Banco Santander Brasil SA ADR (BSBR)	April 2014	18.31%
Centrais Elétricas Brasileiras SA - Eletrobrás (EBR.B)	April 2014	16.56%
Super Micro Computer (SMCI)	April 2014	16.48%
CGI (GIB)	April 2014	16.35%
Contura Energy (CTRA)	April 2014	15.26%
Petróleo Brasileiro SA - Petrobras (PBR.A)	April 2014	13.82%
Gold Fields Ltd ADR (GFI)	April 2014	12.8%
EQT (EQT)	April 2014	12.71%
CH Robinson Worldwide (CHRW)	April 2014	11.74%
Clean Harbors (CLH)	April 2014	11.63%
ResMed (RMD)	April 2014	11.55%
Synnex (SNX)	April 2014	11.35%
MPLX (MPLX)	April 2014	10.47%
Suncor Energy (SU)	April 2014	10.41%
Grupo Financiero Galicia SA ADR (GGAL)	April 2014	10.33%
Pearson PLC ADR (PSO)	April 2014	10.22%
LKQ (LKQ)	April 2014	10.22%
Interactive Brokers (IBKR)	April 2014	9.89%
Cheniere Energy Partners (CQP)	April 2014	9.79%
Apple (AAPL)	April 2014	9.73%
Micron Technology (MU)	April 2014	9.56%
Charter Communications (CHTR)	April 2014	9.55%

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