For me, the most effective daily antihistamine has been Zyrtec (cetirizine). After a few years it's lost its effectiveness for me, though. I now take the third-generation version, levocetirizine (available generic) which requires a prescription.

However, I find corticosteroid nasal sprays are far more effective than pill antihistamines. The nasal sprays are awesome because they work for relieving the symptoms of both allergies and non-allergy rhinitis (caused by things like pressure and weather changes and are not triggered by an allergic reaction).

Currently I'm taking a combination of levocetirizine, Fluticasone propionate (Flonase), and azelastine hydrochloride. The latter two are nasal sprays that make up a brand name product called Dymista. The brand name version simply contains both of these drugs together. However, individually they are available in generic versions which are much cheaper (in America at least). So currently I use both sprays (I use them about 15 minutes apart from each other, as directed by my nurse practitioner who got me on these meds in the first place).

You can pick up Flonase off-the-shelf without a prescription in the US. I recommend starting with that and Zyrtec in combination. If that isn't effective, I would ask your doctor/clinic for recommendations on prescription meds, specifically like the things I mentioned above.