Esophageal Cancer: This is the most likely diagnosis given the patient's age, smoking history, and symptoms of dysphagia that are worse for solids than liquids, indicating a mechanical obstruction. The location of the obstruction, just below the suprasternal notch, suggests a lesion in the upper to mid-esophagus.

Esophageal Stricture: This could be due to chronic gastroesophageal reflux disease (GERD) or other causes of chronic esophageal inflammation, leading to narrowing of the esophagus and difficulty swallowing solids.
Achalasia: A motility disorder of the esophagus characterized by the inability of food to pass through the esophagus and into the stomach, often presenting with dysphagia to both solids and liquids, but can initially present with solid food dysphagia.
Esophageal Ring or Web: These are mucosal structures that can cause intermittent dysphagia, especially to solids, and are more common in the upper esophagus.

Foreign Body Obstruction: Although less likely in an adult without a history of ingestion, it's crucial to consider, especially if the onset was sudden.
Esophageal Perforation: This is a medical emergency that could present with severe chest pain and dysphagia, among other symptoms, and requires immediate attention.

Eosinophilic Esophagitis: An inflammatory condition of the esophagus that can cause dysphagia and food impaction, more common in younger patients with a history of atopy.
Scleroderma: A systemic disease that can affect the esophagus, leading to dysmotility and dysphagia, but typically presents with other systemic symptoms.
Zenker's Diverticulum: A diverticulum of the mucosa of the pharynx, just above the upper sphincter of the esophagus, which can cause dysphagia, regurgitation of food, and occasionally, aspiration.