Which better omnaris or nasonex (mometasone)?

Personal preference . They both work well. It is personal preference. Get a sample of both from your doctor if you can and try them.
Either. Both Omnaris (ciclesonide) and Nasonex (mometasone) are water-based topical nasal steroid sprays indicated for the relief of allergic rhinitis. Both are effective and neither has a safety advantage over the other. If price is a factor, go with the least expensive.