Both the things are important.for example if you eat food and after that do not drink water how will it go.
In robots.txt we disallow the files which we do not want to show. Well i have first research on Meta robots tags and then i will tell you.
If you want to do Nofollow and Noindex both then use robots.txt file in the Root directory and robots meta tag gives you option either you can do Nofollow or Noindex.
Both are same as robots txt is used to stop web crawler not to crawl particular page or content as meta robots work is also same . The main difference is of structure how to use them both. Working of both robots.txt ant meta robots are same.
They both are best because these are very important for the purpose of crawling a website with all the significant analysis .