Market size
Saudi Arabia has roughly three times the population of the UAE and e-commerce is growing fast — more total demand for most everyday categories.
Competition
Both are far less crowded than the US, and Amazon.sa niches often have page-one listings with weak images and few reviews — beatable with the basics done well.
Language and content
Arabic-first content matters in both; bilingual EN/AR listings convert best. The same listing assets usually work for both marketplaces.
The practical answer
Launch on one (Saudi Arabia for most sellers), get profitable, then expand to the other — the sourcing, listing and ads playbook is identical.
💡 Do not split a small budget across two launches — win amazon.sa first, then copy the playbook to amazon.ae.