I have been travel hacking for years. I checked with a few of my best performing sources on your credit card issue. It is unanimous that the best rewards card for the international traveller is the
Chase Sapphire Preferred. It has an annual fee but no international fees for use abroad and the best bonus in the biz. Second place goes to the Capital One Venture rewards card. If there is an airline you use most of the time, you should investigate their particular offerings as you often get really great bonuses.
Keep in mind that credit gurus never recommend cancelling your longest standing card. It could have an immediate effect on your rating depending on the rest of your profile. It may, depending on you situation, behoove you to keep the Discover active and just not use it. I know that may seem to defeat the purpose of your need, but is worth considering if your rating is important to you.