Benign Thyroid Nodules (e.g., adenomatous nodules or colloid nodules): This is the most likely diagnosis given the description of the nodules as having solid isoechoic and cystic patterns, smooth borders, and a TI-RADS score of 3, which indicates a mild suspicion of malignancy but is more commonly associated with benign lesions.

Follicular Adenoma: A common benign thyroid tumor that could present with similar ultrasound characteristics, including a solid isoechoic pattern and smooth borders.
Thyroid Cyst: Although the presence of both solid and cystic components is noted, a predominantly cystic nodule could still be considered, especially if the cystic component is significant.
Hashimoto Thyroiditis: This autoimmune condition can cause heterogeneous thyroid gland appearance and nodules, but the absence of edema and specific mention of nodules' characteristics makes it less likely.

Papillary Thyroid Carcinoma: Despite the low suspicion based on the TI-RADS score, papillary carcinoma can sometimes present with benign-appearing features on ultrasound, such as smooth borders and isoechoic patterns. It is crucial not to miss this diagnosis due to its potential for malignancy.
Follicular Thyroid Carcinoma: Similar to papillary carcinoma, follicular carcinoma might not always display highly suspicious ultrasound features, making it a "do not miss" diagnosis due to its malignant potential.

Medullary Thyroid Carcinoma: This is a less common type of thyroid cancer that might present with a variety of ultrasound features, including solid nodules with or without calcifications. The absence of calcifications in this case does not rule it out entirely.
Metastatic Disease to the Thyroid: Although rare, metastases to the thyroid gland from other primary cancers can occur and might present as nodules with variable ultrasound characteristics.
Thyroid Lymphoma: A rare malignancy of the thyroid gland that could present with heterogeneous gland appearance and nodules, often in the context of rapid growth or systemic symptoms.