Only a comprehensive evaluation and consultation will provide the answers. Degree of hearing loss, manual dexterity, cost, cosmetic concerns, life style and hearing aid features are all considered when making the decisions that best serve your individual needs.

In-the-ear (ITE): largest of all custom instruments, often easier to handle because of size of batteries and controls
In-the-canal (ITC): smaller than ITE so more discreet but more difficult to insert
Completely-in-the-canal (CIC): tiniest of all custom instruments but require the most manual dexterity to handle. Do not usually have volume controls and may lack other important features available in other sizes like directional microphones
Open ear: "thin tube" design with micro size behind-the-ear processor offers best compromise between performance and cosmetics. High frequency losses well-suited to this model, often eliminating sense of own voice being in an echo chamber.
Receiver-in-the-canal (RIC) : similar to open fit in cosmetic appeal, maybe smaller. May provide more natural sound and less "occusion".
Behind-the-ear (BTE): most power and greatest durability. Appropriate for wider range of hearing losses, including severe to profound. Batteries last longer and easier to change. Controls easier to handle.