Wayfair (W) had the highest return in March 2015 by a large-cap US stock, returning 41.1%.

ASSET	MONTH	% RETURN
Wayfair (W)	March 2015	41.06%
Kraft Heinz (KHC)	March 2015	35.8%
Trip Group Ltd ADR (TCOM)	March 2015	31.11%
Summit Therapeutics (SMMT)	March 2015	25.15%
RBC Bearings (RBC)	March 2015	23.11%
Celsius (CELH)	March 2015	19.06%
Biomarin Pharmaceutical (BMRN)	March 2015	16.47%
Centene (CNC)	March 2015	15.11%
Orix Corp Ads (IX)	March 2015	14.74%
Cooper Companies (COO)	March 2015	14.04%
Novo Nordisk A-S (NVO)	March 2015	13.83%
Comfort Systems USA (FIX)	March 2015	13.29%
CBRE Group Inc Class A (CBRE)	March 2015	12.73%
Elbit Systems (ESLT)	March 2015	12.18%
Five Below (FIVE)	March 2015	12%
ResMed (RMD)	March 2015	11.53%
United Therapeutics (UTHR)	March 2015	11.43%
CoreSite Realty (COR)	March 2015	11.24%
Builders FirstSource (BLDR)	March 2015	10.98%
Steel Dynamics (STLD)	March 2015	10.6%
Pegasystems (PEGA)	March 2015	10.5%
Insmed (INSM)	March 2015	10.34%
MACOM Technology Solutions (MTSI)	March 2015	10.3%
Advanced Drainage Systems (WMS)	March 2015	10.15%
Dycom Industries (DY)	March 2015	10.05%

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