The best routine for the gym is the one that is flexible with your schedule and you actually enjoy. These two factors will contribute greatly to your ability to be consistent with your workouts. Consistency with your workouts and progressing as you perform them finally leads to results.
That being said, there are plenty of great workout program styles one can do to build muscle, lose fat, or build strength. The body composition goals (building muscle and losing fat) will be accomplished through similar style workouts combined with differing nutritional principles, while those looking for strength gains may need to focus on programs that are centered on the idea of specificity.

The answer to this question would assume that the person asking is referring to body part splits. In this case, the way you split your days likely won’t matter too much, as long as you work every body part throughout the week.
There may be some benefit into ensuring you don’t hit chest and shoulders or legs and back on consecutive days, but if you do, it probably won’t be that big of an issue depending on your overall strength levels.

The best thing a beginner can do at the gym is seek out the help of a trained professional to assist them with learning the proper form of each exercise. Practicing the basics and establishing a solid foundation in terms of form will help a beginner lifter remain injury free throughout their life.
If you are not in the position to hire a trained professional, you may want to proceed working out with some level of caution. The same recommendation of practicing the fundamentals still applies. Start off with light weight (the bar on barbell exercises) and record yourself performing exercises.

The best workout routine for true beginners is rather subjective to what the beginner is comfortable doing and their understanding of how to perform exercises.
Their ultimate goal will also play a huge factor as well.
Generally speaking though, beginners can start off performing anywhere between 2-4 workouts per week. These workouts can be either full body workouts or upper/lower workouts.

The best workout schedule to build muscle is a workout schedule that you enjoy and even can be consistent with. In addition to consistency, it would be beneficial to have a higher training frequency if the goal is to build lean muscle mass. You may want to hit each muscle group either directly or indirectly 2-3 times weekly to maximize muscle growth.
Some great splits to look into would be full body workouts, upper/lower workouts, push/pull workouts and push/pull/legs workouts.