Cea mai buna carte de vizita a unei companii o reprezinta clientii acesteia. De la infiintare, Happy Day si-a dezvoltat un portofoliu care include companii private nationale si internationale, institutii, etc.:

ACASA IMOBILIARE, MIRALUCIA, E85 IMPEX, PRYSTIL, WHY NOT, HERA, SARATOGA,
ARCELOR MITTAL, UMARO, CERSANIT, BANCA TRANSILVANIA, HOTEL ROMAN,
HANU ANCUTEI, CONCETA MOBILI,  TOPALL, ROMRELIEF, CONSTRUCT PARTENER,
AGFA MILLENNIUM, ROM TV, CNS, TOPALL TV, BOGARDENS, DENTEXPERT,
MOLDY MOBILA,  MILLENIUM INSURANCE, MAXX COMPUTERS, ETC.