Why would Omnaris be better than Nasonex & can I use these drugs for more than 30 days in a row?

Nasonex contains citric acid and benzalkonium chloride (BKC) in addition to its active ingredient mometasone furoate, Omnaris doesn't contain these ingredients and that's why it's better.

Studies show that corticosteroid nasal sprays containing BKC damages respiratory mucosa, decreases mucociliary activity, and inhibits neutrophil functions... not good, especially for someone suffering from sinus problems (these studies are easy to find via google). Also many people are allergic to citric acid and don't know it; citric acid as a preservative is NOT the same citric acid one gets from citrus fruit (I can eat all the citrus fruit I want but I'm allergic to the preservative-form of citric acid). The preservative-form of Citric acid is derived from a black mold (Aspergillus Niger) and can cause allergic reactions (google "the nasty truth; citric acid")

For me switching from Nasonex to Omnaris, to fight my rhinitis, was like night and day. I found Nasonex to have multiple side effects and not very effective. Omnaris, on the other hand, completely remedied my sinus problem with no side effects whatsoever, I've been using it for years.

I believe, as does my doctor, that Omnaris is superior to Nasonex for what it does not have in it... specifically the two preservatives mentioned above.

Omnaris and Nasonex are both topical nasal steroids. They belong to a class of drugs that are probably the most effective at treating nasal allergies. They usually take about two weeks before their full effect is felt and work about the same. Omnaris is newer and the risk of developing systemic side effects is meant to be lower - this may be the reason your doctor is recommending it. They are both safe to take all year round if necessary.
https://www.drugs.com/nasonex.html
https://www.drugs.com/omnaris.html