Best is defined as, "the most excellent, effective, or desirable type or quality" and when it comes to working out, everyone thinks their approach is the most excellent or effective. With an almost endless amount of workout routines to choose from, one of them has to be the best, right?
The secret is: there is no one best workout routine. There are a few general principles to include in a well rounded routine, but beyond that, the "best" workout routine is the one which produces results and is enjoyable or fun. Best is a relative term. The best workout [for you] is the one that works the most excellent and is the most effective for your own needs. The best workout routine differs from person to person and is based on many factors.
What are your fitness goals?
Before you define what your best workout is, you need to figure out what you want out of your workout. Are you working out for a specific event (marathon, powerlifting, bodybuilding, sport)? Are you working out to improve health and/or physical appearance? Are you working out to be around others and meet new people?
Each scenario above describes a different "best" workout routine. Someone who's training for a marathon is going to have a different best routine than someone who's trying to gain muscle for a powerlifting competition. Once you define your own fitness goals, coming up with the best workout routine becomes easier.
General Principles of a Good Workout Routine
The best workout routine differs based on too many factors to list; a few of those factors include: fitness goals, health status, age and fitness level/expertise. Workouts for different goals require vastly different steps. A marathon training regimen looks alien to a bodybuilder. Still, all good workout routines share a few general principles.
Strength Training. Strength training builds muscle through resistance in the form of weights, bands, machines or body weight. In addition to building muscle, strength training also increases bone density. Strength training should be done 3-5 times per week. The exercises making up a strength training routine should focus on compound movements targeting the major muscle groups: squats, presses, rows, deadlifts.
Cardio. Cardiovascular exercise is activity causing an elevated heart rate for a prolonged period of time. Cardio burns a large amount of calories and improves cardiorespiratory fitness leading to better health, lower body fat and increased mobility. Incorporate cardio into a routine 3-6x per week. Include a wide variety of activities. Good cardio elevates heart rate for a prolonged period of time; examples include: circuit training (a combination of strength training and cardio), running, swimming, biking, stair climbing, rowing and most sports.
Overload. Muscle strength, speed and size only improve when there's a need. If you're always lifting a comfortable weight, the body sees no need to build more muscle tissue. Muscle is very high maintenance tissue; it takes a lot of energy to build and maintain. If there's no need for additional muscle (you're not pushing yourself beyond what you can comfortably do), you'll never see improvements in strength, speed or size. In a strength training routine, constantly increase weight lifted and/or repetitions completed. When you reach a plateau, move to new exercises. In a cardio routine, increase distances and speed and include a wide variety of activities.
Recovery. Exercise creates the stimulus necessary for strength, speed and size gains. Exercise actually tears muscle tissue apart. This damage is repaired during rest and recovery. Muscle only grows during this repair process. If you're constantly tearing muscle tissue apart without providing adequate rest, you'll get weaker instead of stronger, slower instead of faster. Overtime, inadequate recovery time turns into injuries. The amount of rest needed varies from person to person. The body tells you to rest with signs such as: excessive soreness, lethargy or a lack of motivation to exercise. Listen to your body. There's a difference between pushing yourself past your limits and pushing yourself towards an injury. Everyone needs rest periods built into their routines.
Nutrition. Though nutrition isn't technically part of exercise, poor eating habits mask gym results. Calories are important for weight goals (how many calories: calorie calculator) while eating the right food is important for overall health and optimal performance. Combine the appropriate calorie intake with healthy food choices to build a great diet.
Enjoyable. The most important part of the best workout routine is picking activities you enjoy doing. If you hate running but build a routine around a lot of running, it's likely the routine won't be the best one for you. Picking modes of exercise you enjoy make finding the motivation necessary for long term success much easier. Avoid doing what works for others if it's not something you have fun doing.
The Bottom Line
The best workout routine is a unique plan that fits your needs. Avoid buying into gym goers who hock around what works for them onto everyone else. There is no such thing as an absolute best workout routine; only general guidelines which everyone should follow.