Power BI RS

It depends what business needs. Especially compressed data model size, number of datamodel used concurently, number of users, and which features is required.

E.g. you buy few Power BI Pro or Power BI Premium per user licences in cloud, and it can be success.

Or With MSSSQL EE SA, you can build complex platform based on MSSQL DB, SSIS for ingest, SSAS for large PBI models, and PBI RS for Power BI report. From long term usage and in case of large models and many endusers, it will be much better from cost perspective (but maybe with some feature limitations).

Generally for small or short solution is better use cloud Power BI Pro or Premium. For large and complex solution with many users is best option combine on-prem MSSQL/SSAS/PBI RS solution with cloud Power BI Premium per capacity.