The services that will work best for you will depend on your specific use case and your team's level of expertise. Because it takes a lot of effort and ML expertise to build and maintain high quality ML models, a general rule of thumb is to use pretrained models or AI solutions whenever possible -- that is, when they fit your use case. If your data is structured, and it's in BigQuery, and your users are already comfortable with SQL, then choose BigQuery ML. If you realize that your use case requires writing your own model code, then use custom training options in Vertex AI. Let's look at your options in some more detail.