Fitness activities are goal-dependent. There is no one "best" exercise, and generally a balance of training methods is used to achieve specific goals.
There are different modalities to exercise. Many of them are complimentary. All of them hit a rate of diminishing returns in finite time.
What you do (how you train / what your fitness routine is) depends on your goals and needs.
Generally, there are:
• Short-term energy systems training: high-intensity cardio. Characterized by high-intensity intervals, Tabata, fartlek, or similar training protocols. A Tabata workout runs 4 minutes.
• Long-term endurance energy systems training: this can help train the body to more efficiently mobilize fat stores. It's what many people think of as "exercise": long, slow, steady-state activities such as walking, cycling, etc.
• Strength training: high-level resistance training to near failure in the 1-20 reps range, generally. This contains within it additional modalities: strength, hypertrophy, endurance, isolation, compound, plyometrics, speed / Olympic lifts, etc. Also involves progression, periodization, and micro / meso / megacycle training variation.
• Prioreception / fine motor control: not entirely the same thing, but essentially training your coordination and skills. This could be gymnastics moves involving strength and balance, pitching or tennis accuracy, or fine motor control utilized by musicians.
• Mobility work: much of the asana practice of yoga delves into this, but myofascial release (self-induced or received massage), heat and cold therapy, etc., play into this.
• Relaxation, meditation, mindfulness, visualization: different aspects of relaxation, many involving stilling the inner voice. The meditative practice of yoga is an embodiment of this.
• Rest and recovery. Anyone training hard becomes a sleep whore. An eight hour minimum, and often sleep binges of 10-12 hours, aren't uncommon for athletes in serious training.
• Diet. Fueling the engine, specific to your goals, is key. Micro and macronutrients, timing, and caloric content are the major factors.
"Yoga" itself is a multi-form discipline (the eightfold path) of which asanas (poses) are only one component.