Antihistamines are grouped into older (first-generation) types, such as chlorphenamine and diphenhydramine, which commonly cause drowsiness, and newer (second-generation) types, such as cetirizine, loratadine, and fexofenadine, which are far less sedating and are usually preferred for everyday allergy relief like hay fever. Loratadine and fexofenadine are generally the least likely to cause drowsiness, while cetirizine causes drowsiness in a small number of people.
There is no single best option for everyone; people respond differently, and if one does not work well or causes drowsiness, switching to another is reasonable. Non-drowsy antihistamines are usually taken once daily and work better when taken regularly during an allergy season rather than only on bad days.
A pharmacist can recommend a suitable non-drowsy antihistamine based on your symptoms, age, other medicines, and any health conditions, and can advise on use in pregnancy or for children. Always follow the dosing on the packaging. See a doctor if your symptoms are not controlled despite regular use, as you may benefit from adding a nasal spray or prescription treatment.