what's the difference between 最好 and 还是 ?

最好 is like strong advice, 'you better do this out of all other options, it is the best idea'.
最好 also sounds stronger in tone than 还是, which is also usually followed by 吧. Most of the time 还是...吧 is an alternative suggestion to the previous one, 'it is better to do this than what was previously suggested'.