Start with how long you have
Your available days are the first filter. EBC needs 14 days door-to-door. The Annapurna Circuit asks for 15. Langtang fits into 9. Short Poon Hill or Mardi Himal options exist for 5-day windows.
Then think about altitude
If you've never been above 3,500 m, start with something in the 4,000–4,500 m range. Langtang, Mardi Himal, and the Annapurna Sanctuary all fit this profile.
Style matters too
Teahouse trekking means no camping. If you'd rather sleep in a tent and cook on a stove, Manaslu and Upper Mustang have camping options.
