Well it depends. If you are looking to grab a free air ticket to Nepal, Delta  is the the best deal as it requires 40k miles for one way ticket vs 45k with other airlines. In terms of earning bonus, British Airways Visa Signature is the best one at the moment if you spend can spend 20k per year. You can earn 100k which basically means round trip ticket to Nepal for free. Keep in mind, you can have the British Airways credit card to earn the bonus miles and use it with its partners.

Thera are other AMEX , VISA, Chase credit cards which offers at least 30K for sign up.