In a chronic smoker, a highly malignant aggressive and metastatic lung carcinoma is :
Squamous cell Carcinoma
Adenocarcinoma
Large cell carcinoma
Small cell Carcinoma
Cigarette smoking is most strongly associated with squamous Cell Ca and small cell Ca and less commonly associated with Adenocarcinoma.
But small cell Ca is highly malignant & Blood stream metastasis occurs early in the course of this Ca.So the answer is small cell carcinoma. 
Also Remember
M.C Variety of lung Ca in India → Squamous Cell Ca*
M.C Variety in world → Adenocarcinoma*
M.C Variety in young Patients → Adenocarcinoma*
Histological Variety that cavitates → Squamous cell Ca*
M.C Histological variety to metastasi → Small cell Ca* 
Lung to lung metastasis is seen in → Bronchoalveolar Ca (a type of adeno Ca)
Clubbing least common in which Ca → Small cell Ca*
Gynaecomastia is seen in which type of Ca → large Cell Ca*
Thrombophlebitis is seen with which Ca → Adenocarcinoma*
Most common site for metastasis from ca lung → Adrenals* (Ref Robbins Basis 7/e, p 760)
Lung Ca with worst prognosis → Small cell Ca* 
Variety most responsive to chemotherapy → Small cell Ca*
Variety most responsive to radiotherapy → Small cell Ca*
M.C Endocrine Gland to be involved by metastasis → Adrenal*
Variety with best prognosis → Squamous cell CA*
Variety that is central in location → Squamous cell & small cell Ca*
Variety that is peripheral in location → Adenocarcinoma*
Most common variety with Cushing's syndrome → Small cell Ca*
Most common variety with Hypercalcemia → d/t PTH like substance Secretion → Squamous cell Ca*