Amit Amit

Don't know the metrics what you are looking for to conclude the best one cloud over other. If this has to be done anyways, then compare their services.
Wild guess is you are asking to invest time and money in learning which clouds services that can take you to find a job quickly. If this is to ask, then start with AWS since it's market share is more than others as of now. So the more jobs in the current market available are for AWS comparetively. Getting on AWS is easy because of the plethora of learning tools possible.
Learn one cloud service a better way, and you will be able to learn others quickly and in a short time.

Go for cloud technologies, to start with- earn AWS certs and then do one specialisation cert, over time you will learn the tech in demand and also programming skills over language/s of your choice java or Python or go or dot net or  PHP or Node Js.
Good cloud knowledge will take you to get a job in the current market quickly.

Don't know what matrix is there to decide best among cloud. It should be service per se if someone has to do this anyway.
If this task is to decide to choose a cloud service to start learning and the end goal is to find a job, then look at market capture which can tell you the higher number of jobs in the current market and possibly to get the calls. Once you get to know one cloud service well, it is easy to understand other too.
Good to start with AWS since a plethora of tutorials/video/training is available. Top of that AWS is cloud leader means max market share, which in turn implies the number of AWS cloud jobs are higher in the market. Go for AWS first makes sense. Rest, one's interest to follow.

Once you get to know one cloud service well , easy to understand other too. 
Good to start with AWS since plethora of tutorials/videos/trainings are available. Top of that AWS is cloud leader means max market share which in turn means number of AWS cloud jobs are higher in market. Go for AWS first makes sense. Rest, one's interest to follow.