https://blog.rsisecurity.com/challenges-with-cloud-encryption/

I think these methods (RSA, DES, AES) are the most familiar methods for encryption

The most familiar methods includes chaos and quantum-based encryption.

Hard to say "best" as that can vary with how much you are willing to spend and your threat model. Commonly used on the big clouds of Azure and AWS is AES-256:

https://docs.microsoft.com/en-us/azure/storage/common/storage-service-encryption

https://docs.aws.amazon.com/AmazonS3/latest/dev/serv-side-encryption.html

to deal with the problem of people leaving things unencrypted in say a S3 bucket.

You can't think about encryption with out considering key management, and cloud vendors these days provide things like key vaults for key management and either you are they can provide the keys.

Another area for data encryption in the cloud is encrypting JSON for protecting results and queries in transit and for authentication (e.g. OATH2, JWT). I suggestion checking out some of the options for this in RFC 7518:

https://tools.ietf.org/html/rfc7518

Another approach for data protection is data anonymization in the cloud. You make it so that data can be analyzed but Personally Identifyable Information (PII) is protected by a variety of methods. While encryption an be used, there are other approaches that can be used - see:

Article Enhancing Cloud Security Using Data Anonymization

An interesting approach in this area, especially to meet GDPR type compliance but still retaining access to PII is tokenization. This substitutes strings for PII when storing in the cloud. These strings don't have to be assigned algorithmically so there is no algorithm to be cracked - almost like a one time pad for each protected field in a record. See:

https://en.wikipedia.org/wiki/Tokenization_(data_security)

In my opinion AES is the best.

The most familiar methods includes RSA, DES, AES for encryption

RSA is widely used in different applications