It depends on  what all basis do you judge a university, and what all factors do you consider while deciding between universities. According to the placements percentage both college stand at almost the same position.

For the infrastructure and environment wise you need to personally visit the campus and decide by yourself as different people have different likes and dislikes. Both are good, but

• Sastra is good when you scored good in JEE and in your higher secondary.
• Amrita is good when scored less in JEE and cleared AIEEE.
• Sastra is good when you don't want to spend much on studies.
• Amrita is good when you think environment and infrastructure is important.

Choice is your. But both are good universities with recognition.

According to Careers360 analysis, SASTRA University, Thanjavur & Amrita School of Engineering, Coimbatore both have got AAAA+ which says these are the outstanding colleges to pursue engineering programs overall Cut-offs of national / state level Entrance exams, Accreditation and Reward status, Publication record from Elsevier’s indexing database - Scopus so you are advised to consider your eligibility, interest and convenience before you decide anything.

For reference, you can go through the below links -

https://university.careers360.com/colleges/sastra-university-thanjavur

https://engineering.careers360.com/colleges/amrita-school-of-engineering-coimbatore

Good Luck!!!