The United MileagePlus Explorer Card has a $95 annual fee, which is waived for the first year though. Such annual fee is pretty standard for travel rewards credit cards. The other card, the United MileagePlus Club Card has a $450 annual fee. Such high annual fee implies access to travel perks and benefits like free checked bags, priority check-in and boarding and other travel benefits.
If you would like to travel without annual fee at all, try the Discover it® Miles card. There’s no annual fee, 0% intro APR and there are unlimited 1.5x miles on all purchases. All the miles you’ve earned at the end of your first year will be matched if you are a new card member. For example, if you earn 30,000 Miles, you get 60,000 Miles.